Egypt is riven by two powerful political forces: a liberal opposition attached to the country's secular traditions, and an Islamist-led bloc headed by President Mohamed Morsi.
Egypt's opposition, which has called for massive protests Tuesday against a referendum on a new, Islamist-backed draft constitution, has become a formidable force against Morsi.
It includes parties with secular, liberal, leftwing and Christian tendencies, and has united into a broad coalition that poses a direct challenge to Morsi's rule.
Morsi's decision November 22 to decree himself near-absolute powers brought the disparate forces together under the coalition umbrella the National Salvation Front.
Morsi's revocation of those powers last weekend has not shaken the Front, which is now focused on scuppering the referendum. If that fails, some of its parties will work on having voters reject it.
The Front is headed by former UN nuclear watchdog chief and Nobel Laureate Mohamed ElBaradei.
His lieutenants are former Arab League boss Amr Mussa, and a high-scoring though defeated leftist presidential candidate, Hamdeen Sabbahi.
Its ranks notably include the April 6 youth movement that was active in toppling former president Hosni Mubarak early 2011.
The united opposition has shown itself able to rally tens of thousands into Egypt's streets, and has promised to do so again on Tuesday in its campaign against Morsi's constitutional referendum due to be held next Sunday.
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The opposition sees the draft charter hastily written by an Islamist-dominated panel as a retrograde text that undermines human and gender rights, and curbs judicial independence, in the service of a push towards a state under Islamic Sharia law.
THE COALITION OF ISLAMIST FORCES
Egypt's well-organised Muslim Brotherhood, from which Morsi hails, and its political wing, the Freedom and Justice Party, are the backbone of the Coalition of Islamist Forces backing the president's policies.
The Islamist group hosts a sort of alliance of convenience between the Brotherhood and smaller ultra-orthodox Salafist parties. The latter aim to push the more moderate Brotherhood towards its vision of a Sharia-ruled state.
Gamaa Islamiyya, an ultra-conservative Islamist group considered a terrorist outfit by the United States and the European Union, because of attacks on tourists and others in the 1990s before renouncing violence, is also part of the coalition.
Both the Brotherhood and the Salafists are well-organised, implementing social programmes and adept at groundroots mobilisation to promote their views.
Those abilities are now being deployed to defend the referendum and to urge a "Yes" vote for the new constitution, which it sees as a step towards "stability".
Having long languished underground as a banned organisation, the Brotherhood is feeling energised by its legitimacy in power, and by the widespread support it enjoys among the very large poorer segment of Egyptian society.
The Freedom and Justice Party won just under half the seats in parliament in the last elections held between November 2011 and January 2012.
The Salafist parties Al-Nour, Al-Assala and Al-Islah held nearly another quarter of the chamber, giving the Islamists an overwhelming majority before Egypt's high courts dissolved the parliament in June.
The coalition is confident of its own capacity to build demonstrations of tens of thousands of people, and plans to do so on Tuesday to counter the opposition's rallies.