What is history modern history?

There are three schools of thought concerning this:

One is that modern history is from 1950 onward.

Another is that modern history is from 1899 onward

The final one is that modern history doesn't exist as something that is modern cannot exist in the past.

Modern history is the considered the time after the "middle ages", beginning around 1500. Modern history is comprised of two eras, early modern through about 1800 and late modern which is followed by contemporary history. Most of this terminology is in reference to European and American history and their relationship with other continents.

Modern History is only part of history. Modern history is from 1850 onward in some ways.