Complex sentence: The first large wave of Afghan immigrants to the UK were political refugees who were fleeing the 1980's communist regime whilst numerous more came in the early 1990's escaping Mujahideen, the number skyrocketed in the same decade due to the rise of the Taliban in Afghanistan.
Split into simpler sentences: The first large wave of Afghan immigrants to the UK were political refugees fleeing the 1980s communist regime and numerous others came in the early 1990s escaping Mujahideen. The number skyrocketed later that decade due to the rise of the Taliban in Afghanistan.