The huge increase in the United States of shares since the global financial crisis means that it represents nearly two -thirds of the investment market in the world, which raises concerns about whether this hegemony creates a lot of risks to investor portfolios.

Before international competitors over the past half and a half, Wall Street raced largely driven by a gathering in the technology sector – especially artificial intelligence companies – which are now worth nearly all shares in Europe combined.

But the recent decline in technology shares has affirmed the increasing tension over the high assessments in a market that swallowed a greater share of global investors’ allocations.

“If you carry a global follower, when the definition of two -thirds of that is the United States, and a lot in Silicon Valley specifically,” said Paul Marsh, a professor of finance at the London College of Business, which has spent the past 25 years to track the long -term investment returns.

“This means that you are very vulnerable to this huge bet on artificial intelligence.”

The closed revenue in the volume of the balloon in the US stock market has helped since 2010, as the country’s share of the global market value of the markets increased from about 40 percent in the wake of the global financial crisis to more than 64 percent by 2025.

The United States won the title of largest stock market in the world throughout the last century, after it crossed in the United Kingdom – the dominant market during the nineteenth century – by the early twentieth century.

By its peak in the late 1960s, the United States accounted for more than 70 percent of the investment global market, according to UBS Global Investment Returns.

This high point was driven by the post -war economy in America, but also a relative deficiency in the competition: most of the “emerging markets” today were not developing important stock markets.

But the global incident in 1973-1974 severely hit the United States. Wall Street stocks in the late 1960s for more than 20 years, according to Professor of Bronil University for Banking and Finance Services E Philip Davis.

This decline allowed a new global leader to appear, although for a short period: Japan has become the only country in the last century that transcends the United States as the largest stock market in the world. The shift arose at the height of the Japanese asset price bubble in the late eighties, which later exploded.

The end of this speculative obsession has left foreign and local investors skeptical of deeply in the Japanese stock markets, and puts its economy for decades. It was not until last year the Nikkei 225 standard beyond the peak of the bubble era.

“From time to time, financing from bars starts and this happened in Japan. Richard Sella, a professor at the College of Business Administration at New York Stain University, said that people are overwhelming roughness, and everyone feels rich, but then it turned out to be a cards home.

The similarities between the stock market today and these historical incidents make some investors uncomfortable.

“The first question I asked at the present time is about what to do about the US stock market.” This has appeared in every conversation I had this year. “

However, the “amazing stability” to perform the American stock market since 2008 makes it difficult to push this trend, because “those who rejected were wrong several times.”

The S&P 500 has achieved an average annual revenue of about 14 percent since 2010, as it exceeded all other major national standards. This performance was strengthened through the gains of more than 20 percent in both 2023 and 2024, where excitement around Amnesty International pushed the shares of the MEGACAP technology listed in the United States, such as NVIDIA chips, to record high levels.

The beginning of the year 2025 brought a rare episode of the weak performance in Wall Street, where the relatively unpleasant European markets are playing.

The US hegemony is also the result of foreign companies, especially in the technology sector, and the choice of the list in New York in search of higher assessments.

Some investors argue that this trend has brought many of the best companies in the world to the United States and will make the market more flexible in economic shrinkage.

“I can build a completely global portfolio based on American markets,” said Jack Applein, chief investment official at the Crestet Capital Investment Company.

But for others, it is not only the role of the American market, but also its focus in a small number of arrows that ignore nerves. In particular, the skeptics refer to the huge gains of many Silicon Valley giants, which Toristin Selk, chief economist in the Apollo Private Capital Group, said that “exaggeratedly exaggerated.”

The Seven Seven Group of Apple, Alphabet, Amazon, Meta, Microsoft, NVIDIA and Tesla are approximately a third of the market value of the S&P 500 dollars, while the rate of evaluation that was adjusted each year in the early 2000.

“The periods come and go where the bubbles begin to form. We are in today’s bubble in the United States, and a bomb in the world of technology.”

Saudi investors argue that the growth of the strong profits of Big Tech and the capabilities of Amnesty International to stimulate productivity justify the noble assessments of many of the largest companies in the world. Meanwhile, the dumpted commentators draw comparisons between today’s market and the DotCom, which exploded at the beginning of the millennium.

The investor’s confidence in January was shaken when Dibsic in China revealed the advancement of artificial intelligence, using the power of computing much less than the American technology groups, which led to doubt about the need for the vast capitalist expenses made by the seven wonderful companies.

This month, renewed tension has achieved the technology sector, and the US market withdraws a little from its highest levels ever.

This is not the first time that the Wall Street sector has been overwhelmed. In the nineteenth century, the hunger of the railway companies for investment played a major role in the early development of the stock market in the United States. By 1900, they represented more than 60 percent of the market value.

“Artificial intelligence is the wave of the future at the present time, but a hundred years ago the wave of the future was the railway companies. Then we had a wave of every person who buy electricity companies.”

The relative decline in the dominant industry is not necessarily bad news for investors. The investor who occupied the railway shares since 1900 had outperformed the broader market in the United States, according to research conducted by Marsh in 2015. Although the total railway share of the market has decreased with the joining of companies from a large number of other industries.

However, the technical hegemony today – the dominance of the United States – has left many investors tense that the wallet that follows a wide range of global stocks leaves them with a lot of eggs in one basket.

“The bottom line is that if the first page is opened in my financial writing, it says that I must diversify.”

“People look at their holdings.. He asked a very essential question, which is:“ Am I diverse? ”The answer today on this question is not very clear.