Why did the battle of gettysburg happen

The largest battle in north american history. it was between the north and the south because the north wanted the south's cotton and money the north was broke and south was rich. the war had nothing to do with slavery that was just a cover up for the north to blame the south for the war. The north had all the slaves not one slave came to the US under the confederate flag. All of the slaves come under the american flag with the 13 stars on it. That's why the battle of gettysburg happened that's the truth the north lied about the whole war