London (CNN) Boris Johnson, the UK's new prime minister, wants you to know that he loves his country.

Specifically, he wants you to know that he loves the Union between the four nations that make up the United Kingdom of Great Britain and Northern Ireland.

Unfortunately for Johnson, this love is not always reciprocated. During his visits to the four nations earlier this week, Johnson was confronted by a number of protesters who took issue with his "do or die" approach to Brexit. Johnson has not been coy about his commitment to leaving the EU on October 31. And he's made it perfectly clear he would do so without a deal.

In Scotland, he was booed by pro-European and pro-Scottish independence supporters. Nicola Sturgeon, Scotland's First Minister and leader of the pro-Independence Scottish National Party, told local media that Johnson didn't have the "guts" to face Scottish people during his visit.

In Wales, he was criticized for not having a plan to prevent the most severe repercussions of a no-deal Brexit, especially for Welsh farmers. Mark Drakefield, Wales' First Minister, said that Johnson demonstrated a "deeply concerning lack of detail."

And in Northern Ireland, which faces the gravest consequences of no deal -- the erection of a hard border with the Republic of Ireland and the terrifying reality of a return to the dark days of sectarian violence -- Johnson was greeted by protesters holding up signs saying that "Brexit means borders."

He is also personally unpopular in the province after comparing crossing the border to traveling between London boroughs -- glibly dismissing the decades-long conflict in which more than 3,000 people died. His cavalier attitude to the Northern Irish peace process continued during his leadership election campaign when he seemed ill informed about the intricacies of reviving suspended power-sharing arrangements.

This is a problem for a prime minister who is staking his premiership on two things: delivering Brexit, come what may, on October 31 and uniting his country.

Preserving the Union is critical to the party that Johnson now leads, formally called the Conservative and Unionist Party. However, Unionism isn't as fashionable as it once was among the UK's electorate -- and that's become especially true after the Brexit referendum.

"I wouldn't be at all surprised if no deal (Brexit) ends being looked at by historians as the event that breaks up the UK," says Rob Ford, professor of politics at the University of Manchester. Ford explains that the strongest support for Brexit comes from English nationalist voters, who don't care much for the Union. "They regard it as not very interesting. And when they view it as an obstacle to Brexit, they will see it as something to throw under the bus."

So, in England, the most populous and powerful part of the UK, Brexit is more closely aligned to a England-first/Britain-first cause. This is where things get interesting.

Across the Irish Sea, things look very different. The most vocal pro-Brexit support in Northern Ireland comes from Unionists, who see any kind of separation from the UK mainland as unthinkable. If it comes down to the choice of a border between the Republic of Ireland or a sea border with Britain, it's going to be the former, every time.

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On the flipside of Unionism is Irish republicanism, which prioritizes no border between the two Irelands at any cost. The most hardline Irish republicans would ultimately like to see Northern Ireland reunited with the rest of Ireland.

A recent Northern Ireland Life and Times survey confirmed that, in the context of Brexit, people who identify as Irish are still in favor of a united Ireland, while those who feel more British have hardened their opposition to unification. However, the survey also revealed that over the past 20 years, more Northern Irish citizens than ever have come to identify as neither unionist nor republican.

And while this group might not be active cheerleaders for a united Ireland, they are starting to see it as an inevitable consequence of a no-deal Brexit.

Put simply, "people who are already sympathetic to Irish unity say Brexit is making them increasingly in favour of it, while those who already oppose Irish unity say that Brexit is making them opposed," explains Katy Hayward, a senior fellow at the think tank UK in a Changing Europe.

In Scotland, "opposition to independence now lines up with support for Brexit," says Rob Ford. He explains that when the SNP embraced a second independence vote in order to join the EU, Euroskeptic Scots will have thought, "why would we trade rule from London for rule from Brussels?"

This left the field wide open for Nicola Sturgeon and her SNP to become the party of remain in Scotland.

Scotland had a vote on independence back in 2014. It voted to stick with the UK by a margin of 55% to 45%. It was at the time described as a "once-in-a-generation" referendum. Then Brexit happened.

When you consider that 62% of Scotland voted to remain in the EU and that Johnson's Conservative Party is now agitating for the hardest form of Brexit, you start to see why Scottish nationalists are feeling optimistic about a second independence vote.

So, in Northern Ireland and Scotland, the pro-remain majorities (56% and 62% respectively) could well be pulling away from Johnson's unionist embrace. The picture is slightly different in Wales, which voted to leave the EU and doesn't have a strong independence movement.

But what Wales does have is a strong nationalist movement that historically dislikes the Conservative Party and loathes Johnson's no-deal rhetoric. Johnson's biggest problem here is alienating these voters and effectively handing more Welsh parliamentary seats to opposition parties.

A case in point was Thursday's byelection in the Welsh region of Brecon and Radnorshire, when one of his own lawmakers was robbed of their parliamentary seat. Despite a surge for his Conservative party in opinion polls, breathless reports of a "Boris bounce" appear to have been premature.

The Boris Johnson premiership could ultimately be defined then by a fight between nationalist movements. If the early days of his time in power are anything to go by, that means doubling down on the English vote. And as Rob Ford explains, "relative to any other group of nationalists, they're the 600-pound gorilla in the fight between all the UK's nationalists. They can throw anyone else out the ring."

It seems unlikely that Johnson's "do or die" politics can smooth over all four corners of the UK, at least before Brexit is delivered. If an election were to suddenly be called -- something most observers in the UK are expecting -- then appealing to the whole Union might not be a wise electoral strategy.

And if the English gorilla does throw the rest of the UK out of the ring, its smaller siblings might decide not to climb back in. And there's a very good chance that England's voters won't particularly care.

This story has been updated.