The Irish backstop was a protocol in the (un ratified) Brexit withdrawal agreement that would have kept the UK (generally) in the customs union of the European Union and Northern Ireland (in particular) on certain aspects of the European internal market until a solution was found to avoid a hard border. This should not compromise the Good Friday agreement and preserve the integrity of the European internal market. This would only have come into effect if there were no other solutions before the end of the (agreed) transition period. If the UK were to leave the EU without “any agreement” (if the draft withdrawal agreement is not approved by Parliament), Northern Ireland (under the UK) would have different customs and regulatory standards than Ireland (under the EU). This means that customs controls on goods must be imported at the border, which could create a “hard border” with physical infrastructure such as cameras or guard posts. This would undermine the principle of North-South cooperation as defined in the Good Friday Agreement. On 29 March 2017, Prime Minister Theresa May launched the two-year Brexit negotiation process with a deadline set for Article 50 of the EU Treaty.  In response, the other EU countries (EU27) published their “phased” negotiating strategy, which postponed all negotiations on future relations with the UK (the non-binding “political declaration”) until a binding withdrawal agreement was reached, On 10 October 2019, Mr Johnson and Leo Varadkar held “very positive and promising” talks that led to the resumption of negotiations and a week later Mr Johnson and Jean-Claude Juncker announced that they had agreed (subject to ratification) on a new withdrawal agreement replacing the backstop with a new protocol on Northern Ireland.2  The backstop would not apply if the UK left the EU without a deal, but potential border problems remained. After the British Parliament voted to leave the European Union, all parties said they wanted to avoid a hard border in Ireland, in part because of the historically sensitive nature of the border. Border issues were one of the three priorities negotiated in the proposed withdrawal agreement. Following the UK`s exit from the European Union on 31 January 2020, this border is also the border between the EU and a foreign country. The Brexit withdrawal agreement obliges the UK to maintain an open border in Ireland, so that (in many ways) the de facto border is the Irish Sea between the two islands.
The Irish government, in particular, insisted on this “backstop”.   The Irish government and the northern Irish nationalists (favourable to a united Ireland) supported the protocol, while the Unionists (who preferred the United Kingdom) opposed it. In early 2019, the Westminster Parliament voted three times against ratifying the withdrawal agreement, rejecting the backstop. In the following months, the British Parliament refused three times to ratify the agreement. In July 2019, Boris Johnson became Prime Minister of the United Kingdom and leader of the Conservative Party.