The events dialog displays a range of events, usually with a time limit, that you can participate in over the course of the game.
These include visits from traveling merchants who stop in front of your castle, kingdoms available for a limited time such as the Blade Coast, or competitions like the nomad invasion.
You can find more detailed information about an ongoing event by clicking on the question mark in its dialog.
Keep in mind that only active players can earn rewards in alliance competitions like the nomad invasion. Players who haven‘t logged in to the game for a while are considered inactive and therefore go empty-handed.