To split something it to cause it to divide, usually using some type of force that causes it to break. When someone says "split" they are essentially using a different way to say "divide". A country divided into 5 parts and a country SPLIT into 5 parts is virtually the same thing, however, saying "a country split into 5 parts" is more like saying "a country (that has been) broken into 5 parts". In everyday conversation or simplified explanation, it is more informal and casual to say "split" instead of saying "divide", but something that has been split was probably divided by force or broken into parts. Does that make sense? Side note: Splitted is not a word. The word "split" is the same in the past, present, and future tense, with the exception being progressive/continuous forms where you would say "splitting" as in "He is splitting them up" or "We are splitting the cost". =)

not much difference. 'Divide' might suggest a more equal distribution between the parts, and it may also suggest a more careful, thought-out action than 'split'.