system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is marriage equality an issue of state law rather than federal law?

Why is this up to each state? Doesn't that just split America apart?
gpt
*The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.*

That's the 10th Amendment.  Since the Constitution to the US does not explicitly define marriage, it is left to the states to decide.