Tyranny is part of human nature. So I don't know if we "defeated" the "forces of tyranny".
We sure as hell, however, defeated the USSR.
I'm starting to think that many of us in the West have forgotten what it means to defeat someone in warfare (cold or otherwise). All the discussions of the Iraq war the past few years are another symptom of this. Someone bombs a market somewhere and we decide it means we "lost" the Iraq war. Bizarre.
Apparently we've become so good at winning wars that we've started to think that the purpose of all wars we get into is to "defeat the forces of tyranny" once and for all (as if that were possible).
When we defeated the USSR in the Cold War, they lost their Eastern Europe colonies, but their Russian homeland stood strongly in the grasp of the same forces of darkness that have controlled them since 1917. To this day, the KGB and some Russian Mafioso still run the place.
We cut off their right arm, but we didn't cut off their head.
They remain a dangerous enemy. We did not defeat the forces of tyranny within Russia (note - I didn't say that we didn't defeat the forces of tyranny for all time in all places - that I agree is not possible - I said we didn't defeat the forces of tyranny in Russia at that time.)
Similarly, we did not defeat the forces of darkness in Germany after World War I. We forced them to collapse, reform and regroup. That's why we got to fight World War II.
Reagan was one of the great leaders of our time or any time. He understood freedom better than most of us, and was willing to devote his life and great talents to fighting tyranny. Collapsing and morphing the Soviet empire was a great victory. But the Russian snake is not dead, its head is not decapitated and crushed. Rather it is just morphed. And it is resurgent.
I fear for my country. With the Leftist control of much of the media, education and government, we may not be able to mount a full scale war again. This great light of liberty that has shown on this nation for the last two centuries will grow dim for many centuries when that day comes.