MapleStory completed their first service migration on November 10th, 2016. Next time you log into the Nexon Europe Launcher, you will receive a notification to set up a Nexon Global Account.
Your game data will be migrated over a period of time, with each MapleStory migration maintenance. You will not be able to play on the Europe server until your game data has migrated. Until that happens, you will be able to play on the North American server.