Once a Treaty has been agreed to, you can view the active effects of it by going to the Nation Status button. From here, you'll be able to view a summary of all active diplomatic relations that your Nation is involved in, as well as the remaining duration of each.

• Alliance - View all Nations in your current Alliance.
• Wars - If your Nation is at War, this is where you can check the Balance of Power bar for each of your current Wars.
• Vassalships - View your Nation's current Vassals or Overlord.
• Other Treaties - Any current treaty effects that don't fall into one of the above categories can be viewed here.