(A) ** Allied Powers
(B) Central Powers
EXPLANATIONS BELOW
Concept note-1: -Under President Woodrow Wilson, the United States remained neutral until 1917 and then entered the war on the side of the Allied powers (the United Kingdom, France, and Russia). The experience of World War I had a major impact on US domestic politics, culture, and society.
Concept note-2: -The Allies, or the Entente powers, were an international military coalition of countries led by the United Kingdom, France, Russia, Italy, Japan, and the United States against the Central Powers of Germany, Austria-Hungary, the Ottoman Empire, Bulgaria during the First World War (1914–1918).
Concept note-3: -The US entered World War I because Germany embarked on a deadly gamble. Germany sank many American merchant ships around the British Isles which prompted the American entry into the war.
Concept note-4: -Beginning July 28, 1914 with Austria-Hungary declaring war on Serbia in retaliation for the assassination of Archduke Franz Ferdinand, a complicated web of alliances plunges the nations of Europe into war within a month. The United States stays politically neutral.
Concept note-5: -The military alliance that fought against the Central Powers was known as the Allies. Initially this alliance was based around the four great powers of Russia, France, Japan and the British Empire, along with the smaller states of Serbia, Montenegro and Belgium that also went to war in 1914.