It was a chain reaction. Long story short, the countries were pulled into the war because of agreements they had with their allies. This treaty is what caused the countries to enter WWI, to protect and defend their allied countries who were already in the war.
Answer:
The spread of the bubonic plague from Central Asia into Europe decimated the populations but increased opportunities for the survivors. An enormous variety of new consumer goods, agriculture, weaponry, religion, and medical science became available in Europe.
The u-2 spy incident increased the tension between the two nations and helped escalate the Cold War.U-2 flights were a voliation of soviet territory and risked a violent soviet response. Hope this helped:)