to compel; to force; to oblige
The situation compelled us to take up arms in self-defence; Under the force of circumstances, we had to take up arms in self-defence; Circumstances forced us to take up arms in self-defence
I was compelled to stay; it was compulsory for me to stay
compulsory; mandatory; obligatory
Is English a compulsory subject? - No, it is an optional subject
Attendance at birthday parties is not mandatory
It is obligatory to show respect for one's teachers