Saudi Arabia and Iran are two powerful neighbours that are locked in a fierce struggle for regional dominance.
The feud between them is exacerbated by religious differences. They each follow one of the two main branches of Islam - Iran is largely Shia Muslim, while Saudi Arabia sees itself as the leading Sunni Muslim power
Historically Saudi Arabia, a monarchy and home to the birthplace of Islam, saw itself as the leader of the Muslim world. However this was challenged in 1979 by the Islamic revolution in Iran which created a new type of state in the region - a kind of revolutionary theocracy - that had an explicit goal of exporting this model beyond its own borders.