In Greek it was called Frankokratia. In Latin it’s referred to as Latinokratia. And in Venetian it was called Venetocracy. But what is it? Whatever terminology that you wish to use, it refers to the time period after the fourth crusade when the Byzantine Empire was falling apart. During this time, a bunch of city-states were forming from the French (known as Francs), Catalans (conquerors from Spain) and Italian (known then as the Venetians) crusaders. The exact dates of the time period fluctuates tremendously because many city-states were constantly being won and lost all at the same time. However, many historians agree that this period was over in the 14th century when the Ottomans took over famously changing Constantinople to Istanbul during a time period known as Tourkokratia.
Constantinople fell to the Francs during the 4th crusade in April of 1204. In order to get to the Holy Land, the French crusaders had to pass through Constantinople. Despite their best effort, they ransacked and took over Constantinople. At that point, the Francs decided to stay put and not pursue the Holy Land to enjoy all the riches that Constantinople offered. However, the Francs were not good at ruling the area and soon an revolution occured from Byzantine soldiers at Nicea in 1261.
This started what began the period of Frankokratia and the many different wars and establishment of city-states. For example from 1204 to 1230, the Bulgarians were able to capture northern Thrace and establish a city state. The County of Salona was established from 1205 to 1410. Originally part of Thessalonica, it was seized and became ruled by the Catalonians before being taken over by the Ottomans in 1410.
But despite all the conquering and changing of rulership during this time, the Greek people stayed strong. Their main language was still Greek. There were no major changes to architecture, religion, and most of their culture. Because it was so constantly changing no one new culture was able to leave its mark during this time period on this area of Byzantine empire.