The printing press, invented by Johannes Gutenberg, had a really strong impact on European society. Thanks to this invention, books became cheap, durable and extended all over Europe.
As the origins of the Renaissance are in Italy, the printing press helped many Italian authors and artists to spread their Renaissance ideas and writings in the rest of Europe, including the northern parts.
Also, it was very suitable for spreading religious influences (by mass printing of the Bible) and many illiterate people learned how to write and read.
The U.S. entered the Vietnam War in an attempt to prevent the spread of communism, but foreign policy, economic interests, national fears, and geopolitical strategies also played major roles.
