This one often appears near the beginning of an exchange or an argument, and it heralds a big-picture, chin-stroking, dot-connecting answer. (It’s the successor to the even more overtly pedantic formulation: But first, some background.) The question is easy to answer because you can pick almost any moment as the precursor for any other; the links you choose depend on the story you want to tell. Proximate causes proliferate! If you don’t like the first ones you find, keep going — you’ll eventually spot one that suits your needs.