Rome declined due to a series of invasions from outside nations and corrupt government officials.
The Korean War. North and South Korea are still technically at war. An armistice was signed in 1953 to halt fighting, but no final treaty was signed, unlike after World War 2.
United States, NATO allies and South Korea fought against North Korea, who received aid from Chinese forces.
This an example of actual combat during the so-called Cold War between the United States and the Soviet Union between 1945-1991. The two sides had different ideologies (democracy vs. communism), which led to friction.
B). Is the right answer from my opinion.
The major reason Napoleon's invasion of Russia failed was because he attacked at the wrong time.
Granted, summer is generally the time used to start invasions against cold-weather countries (as seen by the invasion of France and Germany in their respective times). However, many of them did not think of a long-term fight, and were generally tied up in the western-half of Russia, before being beaten back by weather, shortages, and the Russians.
~<em>Rise Above the Ordinary</em>