(Supporters of the Muslim Brotherhood's presidential candidate Mohamed Morsy celebrate at Tahrir square in Cairo June 18, 2012. REUTERS/Ahmed Jadallah)

From Libya to the Gulf, the rise of Egypt’s Muslim Brotherhood has buoyed Islamists around the region, but the military’s bid to curb their power has also exposed the fragility of the gains Islamists have made since the Arab Spring.

Banned for decades until Hosni Mubarak’s ouster in the face of popular protest last year, the Brotherhood claimed victory on Monday for its presidential candidate Mohamed Morsy in a runoff against his military rival Ahmed Shafik.

Since emerging from the shadows, the Brotherhood has shown it can draw votes, but remains stuck in a high-stakes game for Egypt’s future against an opponent with the power and the will to change the rules when deemed necessary.

The outcome of the power struggle in strategic heavyweight Egypt, the Arab world’s most populous country, is likely to have the biggest impact in the Gaza Strip, where a Morsy win will give a political boost to the Palestinian Islamist group Hamas.