Why did the U.S. fight a quasi-war with France, 1798-1799?

Answer 1

In 1798-99, the U.S. fought the "quasi-war" or pseudo-war with France becase France was siezing U.S. ships and cargo on the high seas. This was a violation of U.S. neutral shipping rights, and the U.S. was furious over this.
However, the U.S. had signed a treaty with the French during the Revolutionary War, and in this treaty, the U.S. pledged to support France against Britain. The U.S. did not uphold their end of the deal, and that's why France siezed U.S. ships and cargo.
So, all in all, both sides were involved and led to the "war."
The XYZ affair also contributed. France demanded money from the U.S. to cover costs of the war with Britain. Otherwise, France would continue to sieze U.S. ships. America responded by saying "Millions (of dollars) for defense, but not $1 for bribery."
I hope this helps you out!

Answer 2

Because they're French. Do we need a better reason?