Complex sentence: While in the process of writing original music they decided to go on the road for some stage experience as a Metallica tribute band called Metalica UK which by total accident became so successful they ended up touring 40,000 miles in Eurpoe and Aisa over a 7 year period.
Split into simpler sentences: While in the process of writing their own original music they decided to go on the road to acquire some stage experience as a Metallica tribute band called Metalica UK. By total accident the band became so successful that they ended up touring 40,000 miles in the UK, Europe and Asia over a 7 year period.