The only moral way to fight a war, is to fight to win.
There is nothing moral about war. When people come to blows it means that their intellect can no longer support their arguments, and they must use physical means to win the argument. Let us accept this.
Nations can do what ever they feel like doing. There is no international law. If you are a strong nation, you can do more than a weak nation. With no way to enforce laws, there can be no law. Let us accept this.
If we look at the facts, not the rhetoric, The United States of America is the most benevolent power the world has ever seen. After abandoning our imperialist ways in the early 20th century we have made no move to expand our territory by force. We gave up all of the land that we conquered in World War II, and in our other military excursions since then. Japan governs itself. The Philippines govern themselves. Germany governs itself. North Africa governs itself. Korea governs itself. Panama governs itself. Iraq governs itself. These nations we conquered. We could have simply called them our own, as nations have been doing for centuries before the U.S. showed up. We chose not to. Let us accept this.
The U.S. is a flawed nation. Nobody is perfect. No system is perfect. We have our problems. Let us accept this.
After accepting all of the above, ask yourself, what nation should be the ultimate power on Earth? Should the U.S. simply stop its weapons research cut its defence spending back to what other nations spend, and let everybody else catch up?
I say no. I say that the great stability that we see in the world today is because the U.S. is the strongest. Make no mistake, human nature has not changed in the last century. Many nations would like nothing better than to march across the world taking it all as their own. Only the threat of the U.S. prevents them. With out that threat the world falls back in to its pre-WWI phase of warring nations.