Supremacy 1914 is as much about diplomacy as it is about armed combat. Most nations simply do not have the resources to fight a war on every front simultaneously, and so you'll need to choose your friends and foes carefully. For this, you'll need the Diplomacy menu, which is represented by a dove in flight.
Diplomatic Messages
From the Diplomacy menu, you will see a list of all other nations, and the players leading them. From this menu, you can open a dialogue with any player in the match. These Diplomatic Messages, while ostensibly private, may be leaked by enemy Espionage operations, or even by the recipient, if they're feeling particularly sneaky.
From this screen, you can also arrange Trade, change your Relationship to the other nation, or hand Provinces over. Diplomacy is one of the most valuable weapons in your arsenal, so use it wisely.
Newspaper
The Daily European is a daily newspaper, whose front page hosts updates and changes in the political makeup of your map. Here, you can review battles, keep an eye on enemy construction and compare your performance to that of your neighbours.
You can also contribute your own articles to the Daily European via the Write Article option. These articles are public, and represent official government communication - so do try to be polite.
Please also keep in mind, in all cases, that our ToS and code of conduct apply to all diplomatic tools, and abuse will result in action taken against your account.