Whether history teaches us to be optimistic or pessimistic is only a matter of when and where you choose to look.

There have been wars at least as long as there has been civilization - which of course continues to today.
Empires have risen, Persian, Chinese, Mongolian, Ottoman, Aztec, Inca, British, USSR.
Some lasted for centuries, some covered the majority of the world (that the culture knew of).
Every one of them fell, for one reason or another, eventually.

That could give hope that the US, which is extending influence both culturally, politically, and militarily throughout the world, will inevitably follow - but its seems obvious that it will be replaced by another - no matter the ideals in begins in, it will inevitably grow corrupt. They all do.

In the 3rd century BC the Egyptian library/museum at Alexandria contained the collected knowledge of the Egyptian and Greek civilizations, the largest in the world. While the circumstances of its destruction are debated, it was apparently due to some combination of war and religious fundamentalism.

The civilizations of the Mediterranean created, among other things, plumbing, calculus, and democracy (but only for white male property owners) - and at the hight of the Roman Empire, a popular spectator sport involved watching humans fight to the death, and eventually flooding the coliseum to create mock sea battles - but with real weapons - for the entertainment of government and the wealthy.
In the Dark Ages, as Rome fell, much of the infrastructure was allowed to fall to ruins, and everything from libraries to aqueducts was lost - along with the education and intellectual development that had accompanied it, and much already acquired knowledge and technology was lost.
Then came about the forced conversion of people in Europe, Asia, and Africa to Christianity and Islam, as well as wars between the two (the Crusades) - ultimately spreading throughout the world, and, of-course, lasting to the present.
Europe's renaissance consisted largely of no more than the re-discovery of things which had been previously known, but lost.

For every Ghandi there has been a Hitler and a Mussolini. For every Roosevelt and Carter we've had a Regan, A Bush, and a Bush Jr. Lenin's "people's revolution" turned quickly into Stalin's purges.
Che failed to start a revolution, and after all of Chavez's work, today immigrants still work in pesticide laden fields for far less than minimum wage while middle class Americans with far more comfortable lives advocate criminalizing them for it.

For all the noise the anti-war movement made, American troops pulled out because the North Vietnamese won.
In fact, the non-violent success Ghandi seemingly had happened to be at a time when the British Empire was already in decline with Canada, New Zealand, Australia, South Africa, Egypt, and Iraq becoming officially fully independent in (or around) 1931, and their military over extended worldwide - a guerrilla war with Ireland, the aftermath of WWII, and calls (and actions) for independence throughout the British Empire in Asia, Africa, and the Americas. For 40 years India had sought independence, but it was not until these - often violent - worldwide events came along that it was finally granted.
Then, almost immediately, (as British representatives had predicted) the country split, and the potentially violent stand-off between newly formed Pakistan and India (both of which have nukes) has lasted to this day. So much for non-violence.

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