But Americans are also braced for a major energy crisis and a warming planet, according to the survey. More than half, or 58 per cent, fear another world war in the next 40 years and 53 per cent expect a terrorist attack against the United States using a nuclear weapon.

The poll also shows a sharp dip in overall optimism from 1999, when 81 per cent said they were optimistic about life for themselves and their families. The current poll found just 64 per cent were.

Sixty-one percent said they were optimistic about the future of the United States, compared to 70 percent in 1999. And 56 percent predicted the US economy would be stronger in 40 years, compared to 64 percent of those polled in 1999.

The results were compiled from telephone and online interviews with 1,546 adults in April. The margin of error is plus or minus 3 percentage points, according to Pew.

Here are some other findings of the poll: