The central powers were Germany, Austria-Hungary, Bulgaria, and Turkey.

The Triple Entente were Britain and the British Empire, France, and Russia.

The Triple Alliance were Germany, Austria-Hungary, and Italy

Romania, Greece, Belgium, Serbia, Montenegro, Portugal, Italy, and the USA joined the original members of the Triple Entente after the war started.

Turkey and Bulgaria joined the remaining members of the Triple Alliance to form the Central Powers .

Italy left the Triple Alliance and joined the Allies.

The existence and use of the alliance system in Europe is considered to be one of he major causes of World War I.

This from a former History teacher.

A group of countries, political parties or people who agreed to work together because of a common goal. i.e war.

The main allies were France, the Russian Empire, the British Empire United state and the Italy. Note that France, Russia and Britain entered world war one in 1914, as a result of their Triple Entente alliance. Many other countries later joined the Allied side in the war.

The U.S. entered the war as an “associated power”, rather than a formal ally of France and Britain, and maintained that distance throughout the war

http://www.historyonthenet.com/cgi-bin/be_dlctr/be_dlctr.cgi?file=/Lessons/worksheets/ww1/european_alliances.doc

http://en.wikipedia.org/wiki/Causes_of_World_War_I