Think about how you communicate. How do you express a thought or idea to someone? The most common way to do this, of course, is to speak. But speaking comes in lots of different forms. Is there one language spoken in your country, or are there many? Some countries have more than one official language, and there are thousands of languages spoken all around the world. But don't you prefer to be around people who speak your language?
This was the case many years ago in the Scandinavian country of Finland. From 1150 to 1809, neighbor Sweden ruled Finland. Throughout these years, Finns struggled to find a national identity. That is, they were looking for something that differentiated them from their Swedish rulers. Near the end of Sweden's rule of Finland, most everyone with money and power spoke Swedish, while the not-so-fortunate spoke Finnish. This was because Sweden used the Finnish economy to pay for Sweden's many expensive wars.
In 1807, Russia invaded Finland. At the time, Swedish rule over Finland was weak. The Russians easily took Finland from the Swedes. In 1809, Finland officially fell under Russian rule. So the Finns went from one outside ruler to another. But the Finns accepted Russian rule differently.