What nations were present at the conference?

Japan, Britain, France, Italy and USA

What was the purpose of the Washington Naval Conference? 

To adress two major issues: the cost of arms race and to defuse the tension between Japan and the USA in Asia

What were the two agreements that resulted from the conference? 

The Four Power Agreement: USA, Britain, France and Japan. Territorial rights in Pacific

The Five Power Agreement: USA, Britain, France, Italy and Japan. Ration for the size of fleets. No building battleships for 10 years