One of the problems one runs into when researching their family, particularly those researching family from continental Europe and farther east, is how often the borders changed. The video below is a great visualization of that problem – it shows the borders of Europe over the past thousand years.
I don't know who put together the original video, and exactly where the data came from, but it's a very impressive video. I do know that the years being shown at the bottom were added later by someone else, so they probably don't match up exactly to the map changes, but you can take them as an estimate.
One very interesting thing to watch in the video (it helps to focus on one area when you watch) is Poland. A little before half-way through when the years shown are in the late 1500s Poland is massive. It later disappears completely, later emerging again in a much smaller form.
So what do you think? Learn anything that can help your family research?