Building a Globally Diversified Index Fund Portfolio

Why Global Diversification Matters

The case for global diversification in equities is both intuitive and well-supported by evidence. No single country, however economically powerful, can guarantee sustained market leadership indefinitely. Investors who concentrated their portfolios in any single market have periodically suffered dramatic underperformance relative to a globally diversified alternative.

Japan is the most instructive example. In 1989, Japan represented nearly 40% of the MSCI World index. A globally diversified investor had meaningful Japan exposure at the peak. A Japan-only investor had suffered decades of stagnation and decline — the Nikkei 225 did not surpass its 1989 peak until 2024. The UK equity market, once dominant, has underperformed global indices for two decades as the sectors that powered the 20th century economy (banks, oil, tobacco, mining) have given way to technology businesses concentrated in the US.

Global diversification ensures that your portfolio is not fatally dependent on a single political environment, interest rate cycle, sector composition, or regulatory framework. When the US market is expensive and disappoints, emerging markets or European equities may compensate. When UK equities stagnate, US technology may propel returns. No one reliably predicts which market leads; owning them all avoids the need to.

The Main Global Indices

MSCI World

The MSCI World Index covers approximately 1,500 large and mid-cap stocks across 23 developed market countries. It represents around 85% of the free-float-adjusted market capitalisation of those 23 markets. It excludes emerging markets entirely.

Country weights (approximate, as of early 2026): US ~70%, Japan ~6%, UK ~4%, France ~3%, Canada ~3%, Switzerland ~3%, Germany ~2%, Australia ~2%, Netherlands ~2%, other developed markets ~5%.

This composition means that the MSCI World is, in practice, overwhelmingly a US equity fund with meaningful but modest exposure to other developed markets. If you buy a MSCI World tracker believing you have diversified across the globe, you have actually placed approximately 70 cents in every dollar into US companies.

The US weighting reflects US dominance in global equity markets, driven primarily by the extraordinary size and valuation of US technology companies. Apple, Microsoft, Nvidia, Amazon, and Alphabet collectively represent a very large share of global market capitalisation.

MSCI ACWI

The MSCI All Country World Index (ACWI) adds 24 emerging market countries to the 23 developed markets of MSCI World. It covers approximately 2,900 stocks across 47 countries.

Emerging market weighting is approximately 12% of MSCI ACWI, with major country weights including China (3%), India (2%), Taiwan (2%), South Korea (2%), Brazil (~1%), and others.

MSCI ACWI provides a more genuinely global portfolio than MSCI World, though it remains heavily US-dominated (approximately 62% US weight, with EM reducing the US share proportionally). Many financial advisers recommend MSCI ACWI as the default benchmark for a global equity portfolio rather than MSCI World.

FTSE All-World

The FTSE All-World index is the main alternative to MSCI ACWI. It is constructed by FTSE Russell (a subsidiary of the London Stock Exchange Group) rather than MSCI, and uses a slightly different methodology for classifying countries as developed or emerging (notably, South Korea is classified as developed by FTSE but as emerging by MSCI).

The index differences are small for most investors. The FTSE All-World is the benchmark for Vanguard's popular FTSE All-World ETF (VWRP/VWRL), while MSCI ACWI underlies many iShares products. Both are excellent choices for a global equity core.

Regional and Country Indices

Beyond the global benchmarks, index investors can access regional indices (MSCI Europe, MSCI Asia Pacific, MSCI Emerging Markets) or single-country indices (S&P 500, FTSE 100, DAX, Nikkei 225). These are appropriate for deliberate tilts — for example, deliberately overweighting European equities relative to their global market-cap weight because you believe they are cheap relative to the US.

The US Concentration Problem

The approximately 70% weighting of the US in MSCI World is a subject of serious debate among institutional investors, advisers, and academics.

The argument for accepting the US weight: Market-cap weighting reflects collective investor judgement about the relative value of the available equity universe. If US companies are genuinely worth 70% of global developed market equities — because they are more profitable, have better growth prospects, and are better governed — then overweighting them is rational. Deviating from market cap is an active judgement.

The argument for reducing the US weight: A 70% US weighting is not diversification in any meaningful sense — it is a bet on the continued outperformance of one country's market. The US market has outperformed global indices since 2010 primarily because of the extraordinary re-rating of technology valuations. The US market trades at a valuation premium to the rest of the world on most metrics (P/E, cyclically adjusted P/E, price-to-book). If that premium reverses — as it did for Japan in 1990 — a market-cap-weighted global index fund delivers large losses from US valuation contraction.

Many sophisticated investors deliberately reduce their US weighting to something closer to the US's share of global GDP or corporate earnings, rather than its share of global market capitalisation.

A practical middle ground: own a global index fund as the core, but supplement with an ex-US developed market fund (MSCI World ex-US) or European equities to reduce the US concentration without the complexity of separately managing many country positions.

The Emerging Market Question

Emerging markets represent approximately 12% of MSCI ACWI by market capitalisation but a much larger share of global GDP and global population. Whether to include them, and at what weight, involves a genuine trade-off:

The case for emerging markets:

• Faster-growing economies: India, Indonesia, Vietnam, and others are growing at 5–7% annually versus 2–3% for developed markets
• Younger demographics: growing middle classes creating consumer demand
• Diversification: EM equity returns have low correlation with developed market returns in the long run
• Valuation: EM equities have often been significantly cheaper than developed markets on fundamental metrics

The case for caution on emerging markets:

• Political risk: government intervention in markets (China's regulatory crackdowns on technology in 2021), expropriation risk, sanctions
• Currency risk: EM currencies can depreciate sharply, destroying returns for foreign investors
• Corporate governance: minority shareholder protections are weaker in many EM countries; related-party transactions and state interference are more common
• Liquidity: EM markets are less liquid, particularly during crises when capital flees

The decision on EM allocation depends on your investment horizon and risk tolerance. A 10–15% EM allocation within a global equity portfolio is reasonable for investors with a long horizon and an understanding of the specific risks. A market-cap approach through MSCI ACWI provides approximately 12% EM automatically.

China-specific considerations deserve attention. China has been the dominant EM country by weight but has disappointed investors repeatedly through regulatory crackdowns, geopolitical tensions, and economic policy uncertainty. Some index providers now offer ex-China EM indices, and several major asset managers have introduced ex-China EM products. This is an area where investor opinions diverge significantly.

Home Bias: A Universal Mistake

Surveys of investor portfolios consistently find that investors in every country allocate far more to their home country than its share of global market capitalisation would warrant. UK investors hold 20–40% of their equity portfolio in UK equities, despite UK equities representing approximately 4% of global market cap. This is not unique to the UK — US investors under-allocate to international equities; German investors overweight German stocks; Japanese investors overweight Japan.

The causes are well-understood behavioural biases:

• Familiarity bias: investors feel more comfortable with companies and brands they recognise
• Information bias: investors believe they have better information about domestic companies
• Currency comfort: holding assets in your functional currency feels safer
• Employment risk: investors employed by domestic companies already have implicit exposure to the domestic economy through their human capital

The consequences of home bias are real: it reduces diversification, concentrates country-specific economic and political risk, and historically has cost returns for investors in markets (like the UK) that have underperformed global indices.

Correcting home bias is one of the most impactful portfolio adjustments available. Moving from a predominantly UK-equity portfolio to a globally diversified one can be transformative for long-term returns, though it requires accepting that domestic market conditions will affect you less and global conditions more.

Currency Risk in a Global Portfolio

Investing globally means holding assets denominated in foreign currencies. When you buy a global index fund, you hold shares in companies listed on exchanges in USD, EUR, JPY, CHF, AUD, and dozens of other currencies. When you convert your returns to your functional currency (the currency you live and spend in), your returns are affected by exchange rate movements.

In any given year, currency movements can be dramatic. GBP/USD moved from approximately 1.40 in early 2021 to 1.07 in September 2022 — a 24% depreciation of sterling. A UK investor in unhedged US equities gained approximately 31% from currency alone during this period. Conversely, the subsequent sterling recovery reduced the currency benefit.

Over long time periods, most research suggests that currency fluctuations largely cancel out — a currency that weakens significantly tends to recover as purchasing power parity reasserts itself. This is the academic argument for holding global equity funds unhedged.

For a globally mobile investor with spending needs in multiple currencies, the position is more nuanced. If you earn in USD and spend in USD, holding USD-denominated global equities involves no functional currency mismatch. If you earn in EUR and spend in GBP, you already have multiple currency exposures and a global portfolio in USD adds another layer.

Currency-hedged vs unhedged ETFs:

Most global equity ETFs are available in both hedged and unhedged versions. Hedged versions use forward contracts to neutralise the currency effect, so your returns reflect local market performance regardless of exchange rate movements. The cost of hedging depends on the interest rate differential between currencies.

For long-term equity investors, the consensus is: leave global equity funds unhedged. Currency risk averages out over a long horizon, and hedging costs money. The main exception is for investors with a known near-term spending requirement in a specific currency — in which case, hedging reduces short-term uncertainty.

Putting a Portfolio Together

A simple, robust globally diversified index fund portfolio can be built with very few products:

Option 1 — Single fund: One MSCI ACWI or FTSE All-World ETF provides instant exposure to 47 countries. Total cost: 0.2–0.25% annually. This is the simplest approach and entirely appropriate for most investors.

Option 2 — Two-fund: 70% global developed market equity ETF (MSCI World) + 10–15% emerging markets ETF (MSCI EM) + 15–20% bonds. This separates developed and EM allocations, allowing you to adjust EM weight deliberately.

Option 3 — Three-fund with US tilt reduction: 50% MSCI World, 15% MSCI Europe, 10% emerging markets, 25% global bonds. This explicitly reduces US concentration while maintaining developed market exposure.

Adding more funds beyond these increases complexity without necessarily adding proportional diversification benefit. The additional tracking error and rebalancing friction of holding eight separate regional ETFs is rarely justified compared to a two or three fund solution.

Risks

Global index fund investing is not without risk. The global economy can experience synchronised downturns — as in 2008 and 2020 — where diversification across countries provides limited protection. Currency movements in both directions affect the realised returns. Index funds by definition cannot outperform the market.

Capital can fall as well as rise. Tax treatment varies significantly by your country of residence and the fund's domicile. The regulatory and political environment across global markets may change. Past index fund performance is not a guarantee of future returns. Seek professional financial advice before investing.

How Global Investments Can Help

Our advisers work with clients across multiple countries and currency situations. We can help you assess the appropriate level of global diversification for your portfolio, select cost-effective index fund implementations, manage currency risk, and structure your holdings tax-efficiently for your specific residency situation. Contact us to discuss building a globally diversified portfolio.