Look at the following sentences.
Many people fled the city to escape the fighting.
Refugees fled from the city.
They fled the country in 1987.
The family fled from Nazi Germany to Britain in 1936.
I am puzzled by the term flee. As you can see that sometimes flee is followed by no preposition whereas sometimes it is followed by a preposition as above.
How to know that it will and will not be followed by a preposition?
Kindly elaborate it.