The emergence of nationalism and extreme patriotism in the mid 20th century and nowadays is no coincidence of time or a natural process. Both stem from past supression by imperialistic nations, or the imperialistic nature of other nations causing trouble in a region. Looking at the axis powers of the Second World War, we can clearly explain their origin by looking how they have been treated through history. The sucess of Nazism in Germany was a reaction to the sharp unemployment created by forced reparations and the humiliation of Versailles, a treaty imposed by inherently imperialistic nations. To prove this, look at the British empire (Britain), the conquest of american over Natives (America) and the French Empire and their harsh treatment of Germany post war (France). Italy's fascism was also a result of imperialism as the Italians felt cheated by Versailles by the larger powers and wanted to be powerful again. The same can be said about the Japanese fascist like era, which was a result by conflicts with the USSR over Manchuria. And looking at the actions of Japan as imperialistic, we clearly see the atrocities committed in the name of dominance.
Looking at more recent times, imperialism has only caused suffering and more violence. The imperialistic policies of the USSR and America during the Cold War (in which both countries forced their ideals on countries without letting the country decide it's self) lead to the spawn of modern terrorism and extremism, as the Americans funded organisations which would lead to IS and Al Qaeda purely out of ignorance and pride. The American government couldn't accept that they might lose the "number 1" position against another super power and did anything (like aiding global terrorism) to look good. And now that has led to a destablised middle east, in which America lied (WMDs in Iraq) to once again impose their views. And before people challenge this, look at the Iran revolution, a clear example that middle eastern people don't like american involvement and control of their countries. And looking at Russia, we see a clear example in the Ukraine of imperialism ruining the lives or ordinary people as they try to dominate what they want.
These are just a few of the many examples of how imperialism is always bad. I didn't even mention the UK which would take much longer and many other examples.
I am not suggesting that the US and NATO should all start conquering land and justifying it. I'm just saying that in the past, foreign nations have been better off under US control. Examples include the Philippines, Puerto Rico, Guam, the American Southwest, and more. Democracy and guaranteed protection are superior to autocracy and genocide.