Congress has formally declared war only 11 times in US history, the last six instances pertaining to World War II alone (one declaration against each member of the Axis). So technically, America hasn’t fought an “official” war since 1945. Additionally, Congress has authorized the use of force overseas 11 times, which includes the conflicts in Vietnam, Afghanistan, and Iraq (both 1991 and 2003).
It’s been estimated that presidents have used force abroad without congressional approval over 200 times. Notably, every modern president has at some point claimed that the War Powers Act of 1973 — which was intended to restrain their power to unilaterally involve the US in foreign conflicts — is an “unconstitutional infringement upon the power of the executive branch.”