If you saw the ending to reach you can see the ship is named the pillar of autumn and in the beginning of halo 1 the ship the cheif is on is the pillar of autumn, and the ship he blows up is the pillar of autumn so its clear to say that reach came before halo 1
If you saw the ending to reach you can see the ship is named the pillar of autumn and in the beginning of halo 1 the ship the cheif is on is the pillar of autumn, and the ship he blows up is the pillar of autumn so its clear to say that reach came before halo 1