There are two islands: Great Britain and Ireland. Great Britain is made up of England, Scotland and Wales, while Ireland includes the Republic of Ireland and Northern Ireland which belongs to Great Britain. 

When people talk about Great Britain, they mean England, Scotland and Wales. However, when they add in Northern Ireland, the name changed into the United Kingdom of Great Britain and Northern Ireland which is the UK for short. 

The Irish border Brexit backstop

So, after Brexit, the UK, including Northern Ireland, will be leaving the EU, whereas Ireland will remain. So the border between Northern Ireland and the Republic of Ireland becomes a real issue. Both sides committed to avoiding the return of a "hard border," physical checks or infrastructure, after Brexit.

This is where the controversial "backstop" comes in. 

So, how to guarantee that aspiration of a frictionless border? No one wants a hard border between Ireland and Northern Ireland. We'll leave the wall-building plan to President Trump. One way to handle the situation is using technology as a means to check vehicles and people in and out of the EU, but the trouble is that technology just hasn't been invented yet. 

Theresa May came up with the idea of a safety net, which she called it the Irish backstop. The safety net kicks in at the end of the transition period, 2020, and will remain until the UK and the EU can think of a proper way to control that border. 

But what is the backstop? Ah. Well, no-one knows. 

 EU and UK's positions on the backstop

The EU originally proposed a backstop that would mean Northern Ireland staying in the EU customs union, large parts of the single market and the EU VAT system, but that means checkpoints will be established in England, thus creating a border in the Irish Sea which is not fair to Northern Ireland who would feel isolated from the rest of the UK.

While for the UK, any separate status for Northern Ireland from the rest of the UK is seen as potentially damaging to the union as a whole. So Prime Minister Theresa May continually rejected the EU's proposal saying it would threaten the constitutional integrity of the UK. 

She suggested a backstop that would see the UK, as a whole, remaining aligned with the EU customs union for a limited time after 2020. But here's the problem. The UK would still be forbidden from coming up with trade deals with the rest of the world which is the whole point of Brexit.

So maybe Northern Ireland could stay in the Customs Union but not Great Britain? Well, we have to go back to the 1970s to see why this won't work. 

 Civil War: The Trouble

Northern Ireland may well be British, but it's Irish too. Many people in the country want to remain British, many want to be reunited with the rest of Ireland, and that caused years and years of civil war, known as The Troubles. Throughout the 70s and 80s, families have pitted against families, neighbors against neighbors, as Northern Ireland fought over its identity.

In 1998, an agreement was drawn up, The Good Friday Agreement which led to lasting peace in the province, but that agreement is fragile. And many fear that if Northern Ireland has separate rules and customs unions from the rest of the UK, the Good Friday agreement will be shattered, and The Troubles will begin again. 

Theresa May need to be very very careful

And that's something this woman will fight to her dying breath to avoid. Arlene Foster is the leader of the DUP, one of the main political parties in Northern Ireland. Due to Theresa May's disastrous general election in 2017, she needs Arlene and her party to prop up the Conservative government. And when it comes to Northern Ireland, Arlene Foster will be a thorn in Theresa May's side. 

Many fear any Irish backstop might lead to Northern Ireland in effect breaking away from the UK. There's already an issue with Scotland, who are clamoring for independence. Unless Theresa May is very very careful, Brexit might not just see the UK leaving the EU; it may well see the end of the UK altogether.