Syria conflict: 10 moments that drove the crisis forward
Two years after a Facebook page appeared calling for revolution, the uprising in Syria has developed into a full-blown civil war, a humanitarian crisis, and a tangled diplomatic impasse. To understand the full extent of the situation requires constant attention to – and knowledge of– the region.
Karen Leigh, managing editor of news website Syria Deeply, has extensive reporting experience in the Middle East and West Africa for publications including Time magazine and the New York Times. In conjunction with our ongoing live Q&A with Syria Deeply, Leigh has identified the 10 most pivotal points of the crisis, ending with a review of this week's opposition meeting in Istanbul, where she is currently based: 
15 March 2011: A Facebook page name "Syrian Revolution 2011" calls for a protest "Day of Rage".
19 May 2011: The US imposes sanctions on President Bashar al-Assad for human rights abuses. The executive order punished Assad and six other senior Syrian officials. The BBC calls it the first time Assad has been targeted by the international community for its crackdown on protesters.
10 July 2011: Syrian officials announce a "National Dialogue" to advance political reform. Opposition leaders boycott the talks, seeing it as a way to mask the government's continued crackdown on protests.
23 August 2011: Syrian dissidents in Turkey announce the formation of the Syrian National Council. The group is meant to unite a fragmented set of dissidents and opposition groups. It becomes the premier voice of Syrians against Assad, but over time it suffers from internal disagreements and high-profile resignations.
4 October 2011: China and Russia use their veto power at the UN to block potential sanctions on Syria. That creates a rift across global powers that will continue for months – the US and Europe pushing for harsher action at the UN, Russia and China opposing it.
12 February 2012: Ayman al-Zawahiri, the leader of al-Qaida, calls on all Muslims to help overthrow Assad. Al-Qaida, searching for relevance in the Arab spring, positions itself on the side of the protesters. A contingent of Al Qaeda linked groups join the fight against Bashar al Assad – which then bolsters his argument that the revolution is led by "terrorists".
13 July 2012: Syria moves some of its chemical weapons out of storage, US officials tell the New York Times. Syria's stockpile of chemical and biological weapons, believed to be one of the largest in the world, are a major security concern. US officials worry Assad might use those weapons "in an act of desperation".
30 August 2012: Syria's government bombs bread lines in Aleppo. Human Rights Watch documents a series of bombings, from the air and from heavy artillery, killing and maiming scores of civilians over the course of several weeks. It added that "both reckless indiscriminate attacks and deliberately targeting civilians are war crimes".
5 October 2012: Anti-aircraft missiles trickle in. After many months of impotently filming bombs falling from the sky, rebels started to find some success in shooting down planes and helicopters. Fighters have also surrounded a number of military airports and organized their disparate groups in order to cut off supply lines in the north of the country.
19 October 2012: Conflict spills over with deaths in Turkey, Lebanon and Jordan. Wissam Al-Hassan, the intelligence chief for Lebanon’s Interior Security Forces, was assassinated in Beirut. Al-Hassan was aligned with political parties who are opposed to the Assad regime and he recently uncovered a plot hatched in Damascus for terrorist attacks in Lebanon. Tit-for-tat shelling on the Turkish border dominated news early in October after a family was killed in a Turkish border village.
Week of 30 May, 2013: This week's disastrous opposition meeting in Istanbul, which all but obliterated any goodwill or support the National Coalition had among Syrians and to an extent, the international community.
For complete background, refer to Syria Deeply's complete timeline. If you have more questions, you can leave them in our Q&A tool to be answered by Leigh along with the Guardian's Tom McCarthy and Dan Roberts on Friday, 1 June, from 11am-12pm ET/4am-5pm BST. 