About a year ago, an investment newsletter picked up an interesting factoid that was in the Swiss National Bank's accounts.
It turned out that the Swiss National Bank owned about $80 billion in US stocks and about $20 billion in European stocks.
How did this come about? Well, the Swiss Franc is considered "safe", so people around the world tend to sell their own currencies and buy Swiss Francs and park the money in a Swiss bank in times of uncertainty such as during the Great Financial Crisis, the eurozone crisis, the migrant crisis and the Brexit crisis. But Switzerland is only a small country with 8.3 million people. They literally can't cope with about a billion investors elsewhere buying their currency - it sends it shooting sky high which makes the real economy of Switzerland suffer.
So the Swiss National Bank printed swiss francs, and then sold them to buy dollars and euros. In other words they were trying to lean in the other direction of the investors. So as investors were selling dollars and buying CHF, the Swiss were selling CHF to buy dollars to cancel them out and prevent the Swiss franc from rising.
So far so good - but what to do with the dollars they bought? They parked some in US treasuries, and parked the rest in US stocks. As at March 2017 it owned 19 million shares in Apple, according to the Swiss National Bank account, which was about 3% of Apple shares.
However, in the last year, the Federal Reserve Bank of the USA has been increasing interest rates. Rates are now 1.75% compared to the minus 0.75% the Swiss National Bank rate. (The Swiss were so desperate to discourage people from buying Swiss Francs that they made their rates negative). This has taken the pressure off the Swiss Franc - it's attractive to hold dollars again, especially as the US economy looks like it is booming.
That means the Swiss National Bank no longer needs to print so much and sell francs for dollars. And that means they no longer have new dollars to park in US stocks.
That lack of buying pressure means that normal conditions have returned in the stock markets. There is no longer a central bank buying everything, now it's just investors and speculators. And of course investors think tech stocks are overvalued and are selling. And the price of tech stocks is going down.
When they write the history books, they'll look back on the last decade of investment as being one of the most manipulated in history.