4 because it says that they were fine before them
Answer:
IN ORDER
3.Arabs come into North Africa.
1. Islam spreads to western and southern of Africa.
2. All of North Africa comes under Muslim rule.
4.The gold-salt trade flourishes on the trans-Saharan route.
The answer is the North Vietnamese took over the South Vietnam spreading communism Southward and this proved the domino theory (if one country come under the influence of communism, the surrounding countries would follow).
Download socratic its a huge help