Whay made the fear of communism real?​

The First Red Scare was during World War One when the Bolsheviks had successfully overthrown the Tsar Monarchy and provisional government. Later on after World War II and during the Cold War, many tensions started growing between the US and Soviet Union. This had started a second Red Scare in the American populace. The Soviets had amazing spy networks among ordinary American life. Americans were not only scared that the Soviets had nuclear weapons to rival that of the US but even their next-door neighbor could be a spy. This caused mass hysteria and events such as McCarthy's purges would single out any individual who "seemed" Communist. The levels of paranoia skyrocketed and sent the US into division and chaos.

The red scare in 1919 and again in WWII happened as a result of the Bolshevik revolution in Russia which made people associate unions with socialists to communists which J Edgar Hoover directed Mitchell Palmer to conduct Palmer Raids to crack down on "suspected communitsts".

helped the Aztec farm more productive - chinampas

helped the Inca travel long distances and communicate with their neighbors - rope bridges

helped the Maya view astronomical phenomena such as eclipses with the naked eye - pyramaid at Chichen Itza