The United Kingdom (Great Britain) is/was a huge imperialistic country. Great Britain has overtaken more countries than some are able to count. Here are a few, United States, India, and South Africa.
France also was a huge imperialistic country. They overtook a couple of places as well, right along with the United Kingdom. They took places like, West Africa, Haiti, and certain islands in the Caribbean.
The next two was just more recently that they gained the idea of Imperialism. Like, China, for example. Just in the year 2000, they used Imperialistic ideas. They are one of the oldest empires to date, and they used to use Imperialistic ideas a lot more than they do now. But, just in the year 2000, they overtook certain parts of Africa.
Lastly, the United States. They have use the ideas of Imperialism, for a while. But, here are a couple of countries overtaken by the U.S. We took Hawaii in 1893, and it was stated as the 50th state of the Union. Just several years later, we took Puerto Rico, but we never stated it as a state of the U.S. We took Puerto Rico in 1898!