Parliamentary Recording Unit / AP

Updated on December 2 at 5:33 p.m.

Britain’s House of Commons has begun a 10-hour debate that will end in a vote on whether the U.K. should expand its air strikes against the Islamic State from Iraq to Syria.

At issue is a motion that calls the Islamic State, which is also known as ISIS, ISIL, or Daesh, “a direct threat to the United Kingdom” and supports “military action, specifically airstrikes, exclusively against ISIL in Syria.”

How is the vote likely to proceed?

Lawmakers are easily expected to vote to approve the government’s motion. Here’s the BBC:

According to BBC research, of the 640 MPs expected to vote, 362 MPs are in favour of the motion while 175 are against. Of the remainder, 19 are "leaning to" supporting the government, three are "leaning against" while 80 are undecided.

Most of the 330 Conservative MPs are likely to vote for the motion, as are about 90 Labour MPs (of 231 in Parliament), the Liberal Democrats, and Democratic Unionists.

Who are the main opponents?

Some members of the opposition Labour Party, including Jeremy Corbyn, its leader, are against Britain’s new role in Syria. The motion is also opposed by some members of the Scottish National Party. But the overall numbers are small: 110 members of Parliament from six parties say they oppose the action.

The public is also divided. A YouGov poll released Tuesday showed support for the air strikes has fallen sharply. Here’s more:

Last week, 59% of Britons backed air strikes; now the figure is just 48%. That eleven-point decline equates to five million electors. The number opposed is up eleven points, from 20% to 31%.

Much of the opposition stems from lingering resentment over Britain’s involvement in the Iraq war in 2003. But the government’s motion explicitly rules out the use of ground forces against the Islamic State in Syria.

How did we get here?

The Arab Spring inspired protests against the Syrian government that were crushed by President Bashar al-Assad in 2011. That eventually resulted in opposition groups taking up arms against Assad. The Islamic State, which until then had been consolidating in neighboring Iraq, swept into the security vacuum and seized territory. At its peak, the group controlled 55,000 square kilometers across both countries—an area slightly smaller than Croatia. Although the Islamic State has lost some ground in Iraq, it remains strong in Syria and carries out attacks around the world, most recently in Paris on November 13—an attack that prompted Wednesday’s vote in Britain’s Parliament.

The situation in Syria is complicated by the involvement of the U.S. and its allies, including Britain, on one side, and Russia and Iran on the other. The West says Assad must step down if Syria’s civil war is to end. Russia and Iran, allies of the Syrian leader, want him to stay in power. The U.S. and some of its allies are already carrying out air strikes agains the Islamic State in Syria (and also in Iraq). Britain, which is part of the Iraq operations against the Islamic State, would join those efforts in Syria after Wednesday’s vote. Russia is carrying out its own air strikes against the group, but it’s also targeting other rebel groups opposed to Assad, including some backed by the West and its allies.

Nearly five years after it began, the Syrian civil war shows no sign of ending, Assad remains firmly in charge, more than 200,000 people have been killed, and 4.2 million Syrians are now refugees. It’s unclear what Britain’s involvement will change.

You can watch the debate here:

The vote is expected at 10 p.m. local time (5 p.m. ET).

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