Before Rip falls asleep, he lives in the Thirteen American Colonies, under the rule of King George III. Since Rip is not really concerned with politics, he doesn't realize that there is revolution impending, nor would he have cared to join the army to fight for his own freedom. Instead, he continues to walk through the woods and eventually misses the entire American Revolution while asleep. His reaction to this is minor compared to his relief at his wife's death:
Rip, in fact, was no politician; the changes of states and empires made but little impression on him; but there was one species of despotism under which he had long groaned, and that was -- petticoat government...
(Irving, "Rip Van Winkle," bartlby.com)
This shows how disconnected Rip was from the real-world issues that dominated public discourse during those years. While he was only concerned with local gossip, the major thinkers of the time were creating a plan to declare independence from monarchy; Rip would have been used as a soldier, but lacked the thought and depth of character to have been any more involved. By sleeping through the war, Rip shows his shallow nature; he cares less about the drastic change to his entire society than about the loss of his friends, and is happy to find that he no longer has to listen to his wife complain about his lack of personal responsibility.