The context of the origin of the US’ pledge of allegiance is it came shortly after the end of their Civil War when there was still a lot o political tension. A desire was born to instill national loyalty in children.

“Historians point to surges in American patriotic oaths and pledges to the flag after the Civil War, when tensions surrounding political loyalties persisted, and in the 1880s, as rates of immigration increased dramatically”

However, today as mentioned by another commenter, students cannot be legally compelled to recite the pledge, nor punished for not reciting the pledge as decided by the Supreme Court in 1943 using the first amendment as the base.