The French Republic was a republic (the 1st->4th republic)but it was still an overseas colonial empire until after WW2 (the 5th republic was formed after WW2 and it stopped being a colonial empire).
Somebody said that the British empire was democratic above... that is not quite true. The "K" in the UK means Kingdom. It's a kingdom because the head of state is the monarch. You call a republic as such because the head of state is a republican denomination (like President) or in the case of the SPQR-> Consuls.