That would be the Berlin Wall, in 1989.
A bit of background: The girls and I read about the Marshall Plan in Story of the World, volume 4, today. The chapter details how the Allied Powers divided Germany into two counties: West Germany as a democracy, to please England, France, and the United States; and East Germany as a communist state, to suit the Soviet Union.
Travel between the two countries was quite easy until the communists noticed a large dip in their population, particularly among the more educated set: doctors, university professors, lawyers, and the like. In 1961, in the middle of the night, a barbed wire fence was erected through the middle of Berlin. Overnight, families, friends, and neighbors were divided, prohibited from visiting one another. Over the years, a more permanent structure went up, a concrete wall 14 feet high.
But in 1989, that wall came down.
I remember this event. I recall watching on TV the jubilant Germans dancing in the streets, chiseling away at the wall, hugging one another and crying. So I immediately thought: YouTube.
There are quite a few short videos of such celebrations, some TV news reports, and some longer documentaries available on YouTube. Tiny Girl and I watched several. She herself watched a 40-odd-minute documentary and enjoyed it very much. Here's the link.
As always, do not turn your children loose on YouTube. Comments are not mediated, and foul language abounds. But what a wonderful resource for recent historical events!