Yemen hasn’t always been one country. Up until 1990, it was two: North Yemen and South Yemen. The south included cities such as Aden and Mukalla while Yemen’s current capital Sana’a was in the north.
Today, tens of thousands of people in Aden held a protest against Yemen’s ousted president Hadi. The people are unhappy with the president for sacking their provincial governor and a cabinet minister. The president is seeking to unify his country while both the governor and minister were part of the Southern Resistance and supporting a separate South Yemen again.
Formerly Marxist South Yemen merged with the North in 1990. Secessionists failed in a civil war in 1994 to reverse the unification, but secessionist sentiment has picked up again in recent years.
Separatists accuse Hadi’s government of failing to provide public services to Aden nearly two years after local fighters, backed mainly by forces from the UAE, expelled Houthis in 2015.
The flag you see the protesters flying is the flag of South Yemen.