When the European powers started to colonize North America, the English were starting their Empire and slowly gained maritime supremacy. That allowed the British Empire to boot out the Spanish, the Dutch (New Amsterdam), the Swedes (New Sweden) and The French (Canada) from the original colonies, and later on the Americans themselves finished the job with guns or dollars (Alaska and Louisiana). So English became "de facto" the official language, except in the North-East and the South, where French and Spanish managed to hold on.