OK, I'm going to give you that one given the first sentence in that section. It might have been clearer still if you'd said "peak of hubris during that time" but that might be quibbling.
I would argue that waiting to see how many lives were lost isn't the best indicator of hubris. In the case of both the Indian Removal Act and the Mexican-American War, the initial reasoning never got much past "It's yours right now but we're gonna kill you and take it from you. Because we can."