English had the misfortune of having its spelling standardized just as the language was going through a major change in pronunciation, such that many spellings today faithfully reflect the way the words would have been spoken 400 years ago. English also has a tendency to borrow foreign words, but preserve both the foreign pronunciation as well as the foreign spelling. As a result, English spelling is a mess!
Numerous reformers have attempted to reform English spelling to more closely reflect modern pronunciation, but not always with much success. In eighteenth century America, there were some strong spelling reform movements, which account for some prominent American/British spelling differences, like color vs. colour, theater vs. theatre, and aluminum vs. aluminium.
If you are interested in more about the history of the English language, I recommend The Mother Tongue: English and How it Got That Way by Bill Bryson.