Complex sentence: Successful strikes in the early 1970s resulted in wage improvements but as the market for UK coal declined and collieries closed, tension between the miners and the government increased and in 1984 a large scale strike started.
Split into simpler sentences: Successful strikes in the early 1970s resulted in wage improvements. However, as the market for UK coal declined and collieries closed, tension between the miners and the government increased and in 1984 a large scale strike started.