"The Irish border wasn’t always so invisible. Between the 1960s and the 1990s, during a period of cross-border sectarian fighting known as « The Troubles »¹, the heavily-fortified border between the Republic of Ireland and Northern Ireland was far more distinct, outlined by military checkpoints, watchtowers, and customs posts".

¹ The Troubles refers to a violent thirty-year conflict from 1968 to 1998. At the heart of this conflict was the status of Northern Ireland.

Source : The Atlantic, « Will Brexit Reopen Old Wounds Between Ireland and Northern Ireland ? », August 3, 2017. https://www.theatlantic.com/international/archive/2017/08/northern-ireland-hard-border/535545/

"The Irish border wasn’t always so invisible. Between the 1960s and the 1990s, during a period of cross-border sectarian fighting known as « The Troubles », the heavily-fortified border between the Republic of Ireland and Northern Ireland was far more distinct, outlined by military checkpoints, watchtowers, and customs posts.

More than three decades of fighting between Unionists (predominantly Protestant) advocating for Northern Ireland to remain part of the UK and the Republicans (predominantly Catholic) advocating for the North to join the Republic of Ireland culminated in the Good Friday Agreement. This 1998 accord brought an end to the conflict and established a system in which power between the Unionists and the Republicans would be shared. As the fighting between the North and the Republic receded, so did the militarized frontier that once divided them.

« Now if you travel between the Republic of Ireland and Northern Ireland, it’s like driving from New York to Connecticut- you just keep going », Senator George Mitchell, the primary architect of the Good Friday Agreement, told me. « In fact, it’s hard to even know it now".

Source : The Atlantic, « Will Brexit Reopen Old Wounds Between Ireland and Northern Ireland ? », August 3, 2017.

Perhaps the most discernible aspect of the border between the Republic of Ireland and Northern Ireland is just how indiscernible it is.With few signposts marking the end of one jurisdiction and the beginning of another, travelers going between the two rely on subtle clues indicating they’ve crossed from one country into another- the changing color of road signs, speed limits switching from kilometers (the Republic) to miles (Northern Ireland), or the more obvious shift between sightings of the Irish tricolor and the Union Jack.

Source : The Atlantic, « Will Brexit Reopen Old Wounds Between Ireland and Northern Ireland ? », August 3, 2017. https://www.theatlantic.com/international/archive/2017/08/northern-ireland-hard-border/535545/

Read one of the following newspaper articles :

https://www.breakingnews.ie/ireland/qa-why-has-the-irish-border-become-a-sticking-point-in-brexit-negotiations-816031.html 

http://www.theweek.co.uk/87818/will-uk-solution-to-irish-border-conundrum-work