How can I know who is at war with whom?

Solution 1:

You can get a lot of information about other civilizations through the Diplomacy Overview screen. You can access this screen through the drop down menu in the top right corner. This menu is accessible by using the button next to the Social Policies button. Once you open up the Diplomacy Overview, click the tab labelled Global Politics. A screen like this should appear, which informs you of the relationships of each opponent:

Solution 2:

From the Diplomacy Overview click on the tab at the top: Global Politics

From here you can see each civilization's :

• Social Policy counts
• Wonders
• war/friendly status for all other civilizations/city states.