The Romans conquered Gaul (modern-day France) and took their language with them. The French conquered England in the 11th century and took their Latin-based language along with them. English is a Germanic language with a Latinate vocabulary. The French nobles introduced their language into England while the peasants retained their old words. Hence, we have many "doublets": Swine (Germanic) vs. Pork (Latin); chicken (G) vs. Poultry (L); cow (G) vs. Beef (L). Likewise, many words were brought into English directly from Latin (color, valor, etc) or created from Latinate roots (independence). For this reason, English has an enormous vocabulary in comparison to most European languages.
