(A) ** Allied vs Central Powers
(B) Union vs Confederacy
(C) Blue vs Red People
(D) NATO vs Warsaw
EXPLANATIONS BELOW
Concept note-1: -World War I had two main factions: the Central Powers, which included Germany, Austria-Hungary, Bulgaria and the Ottoman Empire; and the Allies, which included France, Great Britain, Russia, Italy, Japan and later, the United States.
Concept note-2: -During the conflict, Germany, Austria-Hungary, Bulgaria and the Ottoman Empire (the Central Powers) fought against Great Britain, France, Russia, Italy, Romania, Canada, Japan and the United States (the Allied Powers).
Concept note-3: -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).