The move surprised some analysts because of the long-standing rivalry between the two groups, and likely startled some secularists and liberals.

“Now that this coalition exists, it will dictate the electoral outcome,” said Essam el-Erian, vice president of the Freedom and Justice Party and former member of the Brotherhood’s guidance bureau. Erian said that the coalition is open and encourages others to join…

“This may give them a very solid base in areas they hadn’t previously been strong,” said Elijah Zarwan, an Egypt researcher at the International Crisis Group. The Brotherhood “is taking a long view of Egyptian politics. It’s a very significant switch.”