Complex sentence: This made the question of "national" action a vexed one, and contributed to later disagreement over the question of whether a national strike ballot was necessary; the only nationally co-ordinated actions were the mass pickets at Orgreave.
Split into simpler sentences: This made the question of "national" action a vexed one, and contributed to disagreement over the question of whether a national strike ballot was necessary. The only nationally co-ordinated actions were the mass pickets at Orgreave.