Complex sentence: Although the second world war interrupted his composition (he was organist and choirmaster at London's All Saints, Margaret Street throughout the war) its ending marked the beginning of Lloyd Webber's most prolific years as a composer.
Split into simpler sentences: Although the second world war interrupted his composition (he was organist and choirmaster at London's All Saints, Margaret Street throughout the war). Its ending marked the beginning of Lloyd Webber's most prolific years as a composer.