Complex sentence: Kal-L fought against evil, at first on a local level in his base of operations, the American city of Metropolis; later in his career, he would consider first the entire United States, and then the whole world under his protection.
Split into simpler sentences: Kal-L began fighting evil on a local level in his base of operations, the American city of Metropolis. Later in his career he would consider first the entire United States and then the whole world under his protection.