What were the causes of the rise of nationalism throughout the world in the time period 1750-1900

There were many causes, but the main were need for national unification and also absolutist regimes that dominated Europe in 18th Century.

Explanation:

In 1750. there weren't many national states, especially in Europe. Absolute monarchies, such as France, Austria, Russia and Ottoman Empire were not allowing people who lived inside those countries too many liberties. That is why the wave of national revolution started. It is interesting that first such revolution happened in 16th Century in Netherlands, but this new wave started in British colonies in America, and later in France, Austria, Ottoman Empire ...