Answer:
Almost everything led to Voldemort being his main challenge
Step-by-step explanation:
In the first movie, he faced Voldemort and his professor wanting the sorcerer's stone.
In the second movie, he faced Voldemort's younger self.
In the third movie, he faced Dementors and Serious Black but the source of that was also Voldemort.
In the fourth movie, he actually faced Voldemort in his full form and some of Voldemort's death eaters.
It goes on and on but every antagonist in the Harry Potter movie always leads to Voldemort.
Harry also faced people like Draco and Snape