A look at what's next for Scotland with second referendum

FILE - In this Thursday, Sept. 18, 2014 file photo, supporters of the Yes campaign in the Scottish independence referendum cheer with Scottish Saltire flags as they await the result after the polls closed, in George Square, Glasgow, Scotland. Why Vote Again? Scottish voters decided in a 2014 referendum that they wanted to keep their ties to the U.K. rather than become an independent country. The vote wasn’t particularly close, and it’s not clear if sentiments have changed since then. (AP Photo/Matt Dunham, File) (The Associated Press)

LONDON – The unity of the United Kingdom is coming under threat again with Scottish leader Nicola Sturgeon's Monday announcement that she will seek a new referendum on independence in the next two years.

That means a vote on whether Scotland is to remain part of the U.K. is likely to take place in the midst of Britain's fraught negotiations with the European Union about its withdrawal from the bloc.

Britain's decision to leave the EU provided the spark for the second Scottish referendum. Here are answers to some key questions:

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WHY VOTE AGAIN?

Scottish voters decided in a 2014 referendum that they wanted to keep their ties to the U.K. rather than become an independent country.

The vote wasn't particularly close, and it's not clear if sentiments have changed since then.

But Sturgeon says voters made their decisions based in part on Britain's membership in the EU, and that taking Britain out of the EU, the single market and the customs union causes such major changes in Scottish life that a second referendum is justified.

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WHY IS STURGEON SO ADAMANT?

The Scottish leader points out that Scottish voters expressed a clear desire to keep Britain inside the EU in a June 23 referendum, but their voices were drowned out by English voters who want out.

She says she has since put forth compromise proposals that would allow Scotland to retain membership of the EU's single market, but has run into a brick wall.

She says her options are to do nothing and hope for the best, or take an active role in pursuing independence so Scotland can, as an independent entity, seek new trade relations with the EU.

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WILL THE UK ALLOW IT?

Sturgeon needs British government approval before a binding referendum can be held and plans to start the process next week with an eye toward holding the vote in the autumn of 2018 or early 2019.

British Prime Minister Theresa May was clearly hoping there wouldn't be a second independence referendum in the next few years, and she complained Monday that a fresh vote would be extremely counterproductive.

That said, the government is not likely to block a referendum sought by Scotland's legally elected representatives — to do so would seem undemocratic. If it goes ahead, the British government would give the Scottish Parliament the right to hold a referendum.

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WOULD SCOTLAND STAY IN EU IF INDEPENDENT?

Sturgeon hasn't made this claim, asserting only that there is great warmth for Scotland among European leaders.

There are so many variables that it's not at all clear how quickly an independent Scotland could become part of the EU. It would depend in part on when it became independent, and whether Britain was still technically an EU member at that time.

The complex negotiations between the EU and Britain, expected to be near a climax when the Scottish referendum is held, are likely to have a strong impact on the mood of Scottish voters.

If Britain seems to be getting a good economic deal with many benefits, Scottish voters may decide — again — to stay put. But if the deal seems overly harsh, Scottish voters may feel they have little to lose by opting out.

Scotland's leaders believe the country could be economically viable on its own, thanks in large part to significant oil and gas reserves and other natural resources. They point to countries like Norway as possible models.