the North Atlantic.
No, the Vikings did not engage in combat with the Romans. The Roman Empire had already collapsed by the time the Viking Age began in the late 8th century.
Yes, the Romans and Vikings did not engage in combat with each other during their respective periods of dominance. The Roman Empire fell in the 5th century, while the Viking Age began in the late 8th century, so there was no direct conflict between the two civilizations.
The Second World War began in 1939 and ended in 1945 and engaged most of Europe and Asia into combat between the Allies and the Axis powers.
It all started because of the assassination of Archduke Franz Ferdinand. This caused a ruckus and World War 1 began.
2001.
the 82nd Airborne has, by far, the most combat jumps. This began during WWII.
It was unlikely that the powers in England believed the American colonists would be in full revolt. By the time the rebellion began, the British were not fully prepared to fight a war.
around the 1939
Germany and the US
Neutrality; not taking sides. Some American manufacturers and other interests were supplying the Allies though, or doing more business with them than the Central Powers. Germany's targeting the Lusitania turned American public opinion against the Central Powers.
The Persian empire began when Cyrus the Great led a revolt against the Medes.
The Axis Powers: Germany and Italy.