Here’s another reason for global diversification – a US-focused portfolio is increasingly reliant on a few tech stocks like Apple. The iPhone-maker hit record highs last week, with its market capitalisation hovering at around $3 trillion. Consequently Apple now accounts for 7.6 per cent of the S&P 500 – the largest for any single company since at least 1980, says Creative Planning strategist Charlie Bilello.

The top two stocks in the index (Apple and Microsoft) represent a combined 14.4 per cent of the index – again the highest weighting for any two companies since at least 1980, says Bilello.

The top five stocks account for over a quarter of the index – a record share. Mega-cap tech stocks like Apple and Microsoft are profit machines that have earned their respective weightings, but their success really has made the US market a less diversified place than it used to be.