Donald Trump didn't start any new wars. Nor did he continue any old ones because there aren't any. The last time the US started a war was four years before he was born, against Bulgaria, Hungary and Romania.
US governments, particularly the post-WWII ones, have consistently passed laws giving the president more and more emergency powers which, combined with a little creative wording, has given them more and more power generally. The US has changed from having a government dominated by an elected assembly with a subordinate executive to one dominated by one person with very broad power. Russia uses euphemisms for war for propaganda purposes. The US uses them to get around awkward bits in its constitution.
Most of what Donald Trump has done, not just the wars, has used emergency powers. And guess what? Repealing those laws requires passing laws, which require either presidential assent or an anti-veto super majority in congress.