As "The War to End All Wars" or "The Great War" it's hard for us to understand today how profoundly World War I affected the people of Europe at the time. It was such an unprecedented, total catastrophe that they were scared, shocked, and determined never to let it happen again. They believed permanent peace was possible, which is what this pact was all about.
The problem is, renouncing peace as a foreign policy is great, and a nice idea...until you have to go to war, which is sometimes inevitable.
The Kellogg-Briand Pact is also sometimes called the Pact of Paris because it was signed in Paris, France. It was signed in 1928, which was after World War I but has significance relating to it.
World War I was devastating to many countries and the purpose of the pact was to prevent another world war from happening, although another world war did occur. The pact was an international effort.
This pact gets its name from Secretary of State Frank Kellogg and French Minister of Foreign Affairs Aristide Briand. Briand proposed a pact between the U.S. and France but Kellogg was afraid that this would appear as if they were becoming allies and would support one another in a time of war. This is why many nations were invited in signing the pact.
The Kellogg-Briand Pact was made after WWI (not until 1928) and was therefore of no significance to that war. The war helped to cause the pact, but the pact did not impact the war.
The countries who signed the pact were hoping to prevent another war from happening. Because of this, they negotiated and signed this agreement saying that they would renounce war as a tool of foreign policy. They essentially said they would promise never to attack another country.
This, along with the League of Nations, is seen as a sort of naive attempt to end war via treaties.