In the United States, recovery from the financial crisis a decade ago has continued on as one of the longest economic expansions in American history. Unemployment is at a 50-year low. Fueled by this momentum, while ignoring the intense political disruptions of the past two years, the stock market soared to new heights — until the big plunge this week following an earlier slide in February. To be sure, the volatile market will still have its ups as well as downs. But there are many likely reasons for the emergent crack in confidence. To start with, the consequences of the escalating trade war between the United States and China, especially for the tech sector, are beginning to appear. Tighter money and higher interest rates are on the horizon. A troubling level of over-indebtedness globally among companies and countries alike will be a challenge to finance as interest rates rise. While President Trump’s tax cuts have been an immediate stimulus to growth, the commensurate budget deficits they are creating are deeply worrisome for the long term.