If I were to divide US History onto four easy pieces for study, I would pick:
(1588 - 1763) The Colonial Era: From the Spanish Armada to the Treaty of Paris
(1754 - 1877) A New Nation: From the Albany Congress to the End of Reconstruction)
(1862 - 1935) The America of Business: From the Morrill Act to the Wagner Act
(1914 - present) Arsenal of Democracy: From World War I to the Present Day
These are similar to J.J.'s erae, except I included a colonial era, don't see the need to seperate the last two decades into a sperate era as of yet and I made them overlap.
One problem I have is 1989. The world changed when the USSR was no longer a superpower.
The US became the superpower by outlasting everybody else. That both changed our way at looking as ourselves and the world and how the world looked at us.
I disagree. As far as the US in concerned, we merely traded Jihadists for Communists as our boogeymen of choice when the Cold War ended. That change was not a fundamental one in how we perceive ourselves. We are still the shining city on a hill that is best example and guardian of all that is good in Western Civilization. Now while 1989 would certainly be a pivotal and defining event for Europe (and thus European history) it has been but of minor effect on the US (and thus US history). That divergence of the importance of 1989 is part the reason that Western Europe and the US have drifted apart since then.