Difference between words of Europe and America in form of past tense and past participle

There are lot of alternative forms of the past tense and past participle of the many verb. Learnt is more common in British English, and learned in American English. There are a number of verbs of this type (burn, dream, kneel, lean, leap, spell, spill, spoil etc.). They are all irregular verbs, and this is a part of their irregularity.