So, in other words, Britain lost the American Revolutionary war in 1776 and they lost the war of 1812 to.... the United States.
Everything else you're saying are merely notional excuses. America won the wars, that's the indisputable fact, proven by the fact that we exist today as a nation.
We've been kicking butt since day one.
And if we're going to indulge in conjecture, I would submit to you that had the United States NOT won the two wars in question, then Canada and India would never have gained their own independence from the Brits. The American Revolution set in motion a chain of events that led to the end of the British Empire.
On the plus side, we are not going to have to waste a lot of time drawing you out here, are we? Modesty is not an issue.
As far as kicking butt goes, it happened during WW2, mainly because there was no real alternative, but aside from that we don't know about kicking butt because the US has never won a war that wasn't quite asymmetrical- where the US was significantly more powerful- or at least had the aid of powerful allies, strong enough to ensure victory.
The entry of France and Spain into the revolutionary war were key factors in the outcome, like it or not. The war of 1812 started in a pique of rage over the empressment of US sailors, but was soon regretted by many in the US. New England merchants were non-plussed, as they had enjoyed a profitable trade with Britain, and some continued to do so,smuggling goods as the war went on. British blockade ships stifled trade, and land battles were either lost or wasted men and resources to an indifferent outcome. A side benefit of the war, as seen by Washington, was the conquest of Canada, conceived as an easy grab. It was not, and American troops were forced back into their own country. The final indignity came when the US administration had to evacuate Washington, when it fell to British troops, who burned down public buildings before leaving. If your pride is so wounded by events of 200 years ago, you may call it a draw, but more than that stretches historical fact to the breaking point.
After that, the US took on Mexico, a smaller, poorer, weaker nation then in some degree of chaos. Next on the list was Spain, an empire in long decline, the low hanging fruit of the then nations that had something worth taking: some colonies in strategic places. In WW1, the US intervened towards the end, taking on a starving Germany, with the aid of the British and French empires. China and N Korea battle US (and UN) forces to a draw in 1953, N Vietnam effectively evicted the US in 1973. The learning curve has been steepening since, and in Afghanistan and Iraq, victory was declared, and evacuation achieved, before any more unsavory events marred the celebrations.
Empires have tended to go through phases of first being profitable and desirable, to not so much, to an outright drain on resources. Britain can be included here, and by the 1950s it was clear that the empire was going to end. India was already gone, and the dominions were in close, but independent status. There were a number of factors that led to this over time, the US revolution one hardly of note.