This situation led to a deterioration in Polish−Ukrainian relations, and it would result in a flare-up of ethnic tensions both during and immediately after World War II (with the massacres of Poles in Volhynia and Operation Vistula being the most infamous events).

[6] The staff of the latter was arrested by the Soviets in 1939 during the German-Soviet invasion of Poland which started World War II, with the fate of the Polish consul unknown to this day.

The situation changed significantly with the fall of communism, when both Poland and Ukraine became fully independent and could once again decide on foreign policies of their own.

In the emigre community however, the very influential Paris-based magazine Kultura, which was smuggled into Poland and read widely, advocated for a rapprochement with Ukraine, Belarus, and Lithuania.

[8] In September 1989, shortly after the democratic forces led by Solidarity came to power in Warsaw, a group of Polish parliamentarians arrived in Kyiv for the constituent congress of the People's Movement of Ukraine.

This document, in particular, states: "Poles, who consider freedom and independence of the Fatherland as their core values, fully understand the turning point in the history of Ukraine—a neighbor with whom they want to live as equal and close peoples, as well as develop cooperation in everything."

On August 3, 1990, the Senate of the Republic of Poland adopted a special statement in which it gave a political and moral assessment of the Vistula action.

The Senate of the Republic of Poland condemns the action "Vistula", typical of totalitarian regimes, and will try to compensate for the insults arising from it.

On May 18–19, 1992, the first official visit of the President of Ukraine Leonid Kravchuk to the Republic of Poland took place, during which an interstate Treaty on Good-Neighborliness, Friendly Relations and Cooperation was signed, in which it was stated that the countries structures based on the Final Act of the Conference on Security and Cooperation in Europe, the Paris Charter for a New Europe, "will take and support measures aimed at preserving and developing positive traditions of common heritage, as well as overcoming prejudices and negative stereotypes between the two nations.

A further important step in creating an organizational infrastructure for bilateral dialogue was the interstate "Agreement between the Government of Ukraine and the Government of the Republic of Poland on Cooperation concerning the Protection and Return of Cultural Property Lost and Illegally Displaced during World War II" dated 25 June 1996, which defined and specified the subject and scope of mutual cooperation between the parties.

"[9] After the visits of Leonid Kuchma to Warsaw on June 25–27, 1996 and the newly elected President of Poland Aleksander Kwaśniewski to Kyiv on May 20–22, 1997, Ukrainian–Polish relations reached the level of a strategic partnership.

The National Security Strategy of Poland declares Warsaw's support for Ukraine's Euro-Atlantic aspirations, in particular, as part of the continuation of the "open door" policy to NATO.

During the official visit of the Minister of Foreign Affairs Bronisław Geremek to Ukraine on September 15–16, 1998, the parties agreed to intensify joint actions in order to avoid possible negative consequences of EU enlargement.

Bronisław Geremek also noted that his country will continue to support Ukraine's integration aspirations, in particular in gaining the status of an associate member of the EU.

This is due to Poland's vision of its national interests in the context of the basic contours of European security and to the desire to play an important role in a renewed Alliance that adapts to modern conditions.

At the same time, in the conditions of post-orange development there was a need for significant modernization of the structure and filling of the political dialogue between Ukraine and Poland.

For example, cooperation aimed at achieving Ukraine's compliance with the first of the Copenhagen criteria for EU membership ("political" criterion): ensuring the stability of democratic institutions, protection of human rights and the rule of law has become essential.

Ukraine and Poland have signed agreements on academic recognition of documents on education and scientific degrees and on cooperation in the field of informatization.

An important focus of the development of bilateral relations was Poland's initiation of the activation of the Eastern vector in EU policy.

The Polish Foreign Minister stressed that his country intends to implement the ENP in the east with its partners—the Czech Republic, Slovakia, Hungary, Estonia, Lithuania, Latvia, Romania and Bulgaria, as well as with Sweden.

The JV initiative is addressed to six countries: direct addressees – Ukraine, Moldova, Georgia, Azerbaijan and Armenia, as well as technical and expert cooperation with Belarus.

[citation needed] Thus, since Poland's accession to the EU, relations have been filled with new content, and its role as a lawyer and lobbyist for Ukraine's European integration and Euro-Atlantic course has been strengthened.

This was manifested, on the one hand, in support of Ukraine's ideas, and on the other – in the development and implementation of a specific program of EU cooperation with Eastern Europe.

It is the Polish–Swedish initiative aimed at real acceleration of the process of Ukraine's accession (along with other Eastern European countries) to EU integration.

Different interpretations of bitter events regarding Poles and Ukrainians during World War II have led to a sharp deterioration of the relations between the nations since 2015.

[13] Historical issues regarding the Ukrainian Insurgent Army (UPA) and their massacres of Poles in Volhynia and Eastern Galicia remain a contested topic.

A joint declaration on the creation of the Lublin Triangle stressed the importance of intensifying the cooperation between the EU, NATO, and the Eastern Partnership and paying special attention to the development of the Three Seas Initiative.

On 23 February 2022, in response to Russia's escalation of tensions and recognition of the separatist Donetsk People's Republic and Luhansk People's Republic in Russian-occupied eastern Ukraine, Polish President Andrzej Duda visited Kyiv along with the President of Lithuania, and they jointly declared solidarity and support for Ukraine, and called for international sanctions against Russia.

[39] By February 2024, the blockade had expanded to all major crossings including railways, and protestors had spilt some grain onto the ground from train transport.