DAN BALZ, The Washington Post: Well, it's likely to be some strange bedfellows. And it's also likely to take a long time.

Five years ago, it took five days to form a new government. And this time, it could take — it could take a matter of weeks, because the uncertainty is whether to the Conservatives, who are expected to win more seats — they will fall short of majority — may have a greater problem putting together enough for a majority government.

And that might leave it in the hands of the Labor Party, which is expected to run second, but may have more potential allies to form the government.

HARI SREENIVASAN: So, what were some of the factors leading some of these smaller parties to gain in popularity and take away the mandate that either of the two major parties would have had traditionally?

DAN BALZ: Well, there's a couple of things.

The biggest single factor is the earthquake that's happened in Scotland, where the Scottish National Party, which just last year lost the referendum battle to declare independence from the United Kingdom, has been rejuvenated in this campaign. And they're now in a position to win almost every seat in Scotland tomorrow.

Scotland has been a stronghold of the Labor Party. And so that's the biggest single piece. But there are others as well. One is that the Liberal Democrats, which used to be the dominant third party in this country, have seen their support erode as they have been part of the coalition government with the Conservatives.

And then you have the rise of the UKIP, the U.K. Independence Party, which is an anti-immigration, anti-Europe party, which is polling quite strongly. It will end up with very few seats, but it has drained off popular support from the Conservatives in some areas and from Labor in some other areas. And some of the support on the left that Labor might have counted on in the past has gone to the Green Party.

And so you have a real fracturing of a system that over a century or more basically produced stable single-party governments and a strong, stable two-party system, and that has all broken apart in the last few years.

HARI SREENIVASAN: So, from an American viewpoint, are there likely to be any changes in policy or our alliance, regardless of who's in power, and the deals that they have to make to form a coalition?

DAN BALZ: Well, I think that there is worry on your side of the Atlantic over a couple of things.

If this is a Conservative-led government, David Cameron, who's the prime minister, has pledged that he will put forward a referendum on whether the United Kingdom should stay in the European Union. That will create a considerable amount of disruption. There is worry back in the United States about what that means, both in terms of the kind of inward-looking Britain that we will see as they debate their own future, as opposed to being somewhat more robust in the world, and what kind of standing they will have in Europe whether that passes or not.

I think the concern on the other side is that, if there is a Labor-led government, that Great Britain would be less robust of an ally in terms of projecting power with the United States in places around the world, which they have certainly been over many years, although there has been, as you know, a backlash against what happened during the Blair government and during the Iraq War.

So there's concern about the direction of the United Kingdom and Great Britain, no matter which way it comes out. There's a feeling that this is a country that has got more to think about in terms of its own future, where is its place in Europe, is it going to be a United Kingdom, or is it going to break up in the future, with Scotland perhaps leaving? There's a lot of issues of nationalism that have come to the fore in this election.

So, Britain is now looking inward at itself much more than it has in the past.

HARI SREENIVASAN: And so what are some of the implications on a global or foreign policy front of how the U.K. chooses to behave in light of what happens?

DAN BALZ: Well, I think one element will be the degree to which they are prepared to commit military forces in the fight, say, against ISIS or other things like that. Ed Miliband has pledged to continue to keep the fight against ISIS.

But he was very much against taking action in Syria, and used that — used his opposition to the president of the United States as an example of how tough he is prepared to be as prime minister. There have been questions about, is he strong enough to stand up to Putin?

And in one of the interviews that he did earlier this — in the campaign, he said, well, I'm plenty tough. I stood up to the president of the United States on Syria.

So I think there has to be concern about that.

HARI SREENIVASAN: All right, Dan Balz, chief correspondent for The Washington Post, joining us from London, thanks so much.

DAN BALZ: Thank you, Hari.

JUDY WOODRUFF: And we have an online guide to Thursday's election in the U.K. That's on our home page, PBS.org/NewsHour.