The U.S. economy is revving up just as Europe and other major economies lose steam, jeopardizing a rare period in which the world’s largest economies have been accelerating in unison.

The European Central Bank on Thursday took another step toward ending the massive stimulus measures it has used in an effort to boost growth since 2015. But ECB officials also said they would hold interest rates steady through summer next year, a sign that they felt the eurozone economy remains fragile.

In an indication of growing economic vigor in the U.S., the Federal Reserve on Wednesday tapped the brakes again, raising the benchmark interest rate by a quarter of a percentage point and signaling it may quicken the pace of future rate increases because of a strengthening economy and tightening labor markets.

The economies’ diverging paths were expressed most prominently in the euro, which on Thursday suffered its worst day against the dollar in two years. The euro lost 1.88% against the U.S. currency, its biggest drop since the day after the U.K. voted to leave the European Union.

The central bank announcements over the past two days offered the latest evidence that heady growth expectations for Europe and other major economies outside the U.S. might not be achieved, defying analysts who began the year convinced that the world economy’s first synchronized expansion in years would continue.