Explain why there are differences between British & American English

Aside from spelling and vocabulary, there are certain grammar differences between British and American English. For instance, in American English, collective nouns are considered singular (e.g. The band is playing). ... 'Needn't', which is commonly used in British English, is rarely, if at all used in American English.

answers.com says temperate reagions

answerpeople organize large projects such as levee-building;