Hitler and Bush Jr
Both Hitler and Bush Jr invaded countries, against international laws, both failed because they were fought back by very motivated insurgencies and were unable to win the occupied hearts.
Hitler's troops were quicked out by the allies who formed the UN.
What matters is to be able to justify a war. WW2 was easy to justify: liberating occupied countries; GW2 was not about liberating an occupied country.
In fact, I still don't know why Bush invaded Iraq.