Question: What eastern European border was disputed between it's two nations after World War I, was re-established in 1990 as an identical version of its former self, changed only in the name of one of it's nations?

Context paragraphs:
Brazil–United States Treaty: The Brazil–United States Treaty was a military assistance agreement signed in 1952 in Rio de Janeiro between the two countries, with the goal of defending the Western Hemisphere.  Military relations between the United States and Brazil date back to World War II, when Brazil supported the Allied effort in the invasion of Italy in 1942.  Brazil provided troops for the invasion.  On January 3, 1952, The Brazilian government issued decree 30363 establishing new government regulations.  These new regulations allowed for the return of foreign capital that was invested in Brazil and profit remittances on that capital.  Shortly after, representatives from the United States and representatives from Brazil started to negotiate a bilateral military assistance agreement in Rio de Janeiro on January 3, 1952.  The document outlining the agreement between the two countries would be signed on March 15, 1952.  The agreement went into effect on May 19, 1952.  During the time of the negotiations, Major General Charles L. Mullins, Jr. negotiated a separate military plan with the Brazilian Government.  The plan was approved on March 14, 1952 by the Secretary of Defense Lovett.  In a private ceremony on March 15, 1952 United States Major General Mullins and Brazilian General Monteiro signed the military plan that outlined a common defense between the two nations.  The agreement allowed major weapons and training by the United States military to the Brazilian military.  This tenuous alliance governed the two nations bilateral ties during the events of the Cold War.  However, the alliance was short lived, and suffered several major blows between the two nations during the military coup in Brazil in 1964.  During this time the United States still provided military support and training to the side that supported the United States.

Suwałki Region: Suwałki Region (Polish: "Suwalszczyzna" , Lithuanian: "Suvalkų kraštas, Suvalkija" ) is a small region around the city of Suwałki (known in Lithuanian as "Suvalkai") in northeastern Poland near the border with Lithuania.  The territory was disputed between Poland and Lithuania after World War I.  This dispute was the main cause of the brief Polish-Lithuanian War and the Sejny Uprising.  The conflict was later overshadowed by a much larger and more serious Polish-Lithuanian dispute over the Vilnius Region.  The Suwałki Region remains a major center of the Lithuanian minority in Poland.

Back to the Pilot: "Back to the Pilot" is the fifth episode of the tenth season of the animated comedy series "Family Guy".  It originally aired on Fox in the United States on November 13, 2011.  In "Back to the Pilot", two of the show's main characters, baby genius Stewie and anthropomorphic dog Brian, both voiced by series creator Seth MacFarlane, use a time machine to travel back in time to the first episode of the series, "Death Has a Shadow".  Trouble ensues however, when Brian tells his former self about the September 11 attacks, causing the present to be dramatically changed, and ultimately resulting in a second civil war.  The two must then prevent themselves from going back to the past in the first place, but soon realize that it will be much more difficult than they had originally thought.

Canada–United States relations: Relations between Canada and the United States of America historically have been extensive, given a shared border and ever-increasing close cultural, economical ties and similarities.  The shared historical and cultural heritage has resulted in one of the most stable and mutually beneficial international relationships in the world.  For both countries, the level of trade with the other is at the top of the annual combined import-export total.  Tourism and migration between the two nations have increased rapport, but border security was heightened after the terrorist attacks in the United States on September 11, 2001.  The U.S. is ten times larger in population and has the dominant cultural and economic influence in the world.  Starting with the American Revolution, when anti-American Loyalists fled to Canada, a vocal element in Canada has warned against US dominance or annexation.  The War of 1812 saw invasions across the border.  In 1815, the war ended with the border unchanged and demilitarized, as were the Great Lakes.  The British ceased aiding First Nation attacks on American territory, and the United States never again attempted to invade Canada.  Apart from minor raids, it has remained peaceful.

Lithuania–Poland border: The current Lithuania–Poland border exists since the re-establishment of the independence of Lithuania on March 11, 1990.  Until then the identical border was between Poland and Lithuanian SSR of the Soviet Union.  The length of the border is 104 km .  It runs from the Lithuania–Poland–Russia tripoint southeast to the Belarus–Lithuania–Poland tripoint.

India–Pakistan cricket rivalry: The India–Pakistan cricket rivalry is one of the most intense sports rivalries in the world.  The arch-rival relations between the two nations, resulting from the extensive communal violence and conflict that marked the Partition of British India into India and Pakistan in 1947 and the subsequent Kashmir conflict, laid the foundations for the emergence of an intense sporting rivalry between the two nations who had erstwhile shared a common cricketing heritage.

Mixed Service Organisation: The Mixed Service Organisation (MSO) was a civilian arm of the British Army of the Rhine (BAOR) which employed displaced persons as drivers, clerks, mechanics and guards.  Originally formed as Watchman and labour units in the immediate aftermath of the Second World War the MSO employed citizens of Eastern European nations occupied by the Soviets.  These former prisoners of war, concentration camp inmates and forced labourers were left in western sectors of occupied Germany at the end of the war and chose not to return to their countries of origin.  Whilst some displaced persons only worked with the organisation for a short time others stayed until retirement age.  The MSO was organised in a structure similar to British Colonial Units, with a British Commanding Officer and senior Non-commissioned officers operating over a 'native' officer and NCO structure.  Whilst the Transport Service was disbanded in the late 1980s the MSO Guard and Labour Services continued into the 1990s using guest labour from Turkey, Pakistan and other Non-EU Countries.

Foreign relations of Eritrea: The foreign relations of Eritrea are the policies of the Eritrean government by which it administers its external relations with other nations.  Since its independence, Eritrea's foreign relations have been dominated by conflict and confrontation, both in the regional and international arenas.  It has maintained often troubled, and usually violent, relations with its neighbors, including brief armed conflicts with Yemen and Djibouti and a destructive war with its bigger-neighbour, Ethiopia.  At present, Eritrea has very tense relations with neighboring Ethiopia and Djibouti.  Relations in the international arena also have been strained since the last decade, particularly with major powers.  What appeared cordial relations with the US in the 1990s turned acrimonious following the border with Ethiopia, 1998-2000.  Although the two nations have a close working relationship regarding the ongoing war on terror, there has been a growing tension in other areas.  Ties with international organizations such as the UN, African Union, and the EU have also been complicated in part because of Eritrea's outrage at their reluctance to force Ethiopia to accept a boundary commission ruling issued in 2002.

Czechoslovakism: Czechoslovakism (Czech: "Čechoslovakismus" , Slovak: "Čechoslovakizmus" ) is the nationalism of Czechoslovaks and Czechoslovak culture either for which Czechs and Slovaks embrace a Pan-Slavic state in which they function as constituent nations (political form), or for which the two nations form a single West Slavic ethnic group (ethnic form of Czechoslovakism).  Czechoslovakism is based on natural cultural and language affinity of Czechs and Slovaks and has roots in early romantic national movements (works of Ján Kollár or František Palacký).  The idea had been continuously developed and supported by common meetings and organizations like Czech-Slavic Unity (Českoslovanská jednota), where Czech sympathies for Slovaks and their spontaneous reactions on oppression of Slovaks in the Kingdom of Hungary played a partial role.  However, both nations also developed other alternatives like Austro-Slavism, close collaboration with other non-Hungarian nations in the Kingdom of Hungary or pan-Slavic orientation on Russia.  Before World War I, Czechoslovakism was further developed by Tomáš Garrigue Masaryk and Edvard Beneš, based on the premise that Czechs and Slovaks are one people who had become divided due to Austro-Hungarian imperial rule and Hungarian assimilationist policies in particular.  These Czechoslovakists noted that a united Czechoslovak people existed in the historical state of Great Moravia, where the Slavonic tribes of Bohemia, Moravia, and Slovakia were formerly embraced within Great Moravia.  Czechoslovakists typically emphasize secularism to break down the religious divide between Czechs and Slovaks.

Flight and expulsion of Germans (1944–50): During the later stages of World War II and the post-war period, German citizens and people of German ancestry were expelled from various Eastern European countries and sent to the remaining territory of Germany and Austria.  After 1950, some emigrated to the United States, Australia, and other countries from there.  The areas affected included the former eastern territories of Germany, which were annexed by Poland and the Soviet Union after the war, as well as Germans who were living within the prewar borders of Poland, Czechoslovakia, Hungary, Romania, Yugoslavia, and the Baltic States.  The Nazis had made plans—only partially completed before the Nazi defeat—to remove many Slavic and Jewish people from Eastern Europe and settle the area with Germans.  The post war expulsion of the Germans formed a major part of the geopolitical and ethnic reconfiguration of Eastern Europe in the aftermath of World War II, that attempted to create ethnically homogeneous nations within redefined borders.  Between 1944 and 1948 about 31 million people, including ethnic Germans ('Volksdeutsche') as well as German citizens ('Reichsdeutsche'), were permanently or temporarily moved from Central and Eastern Europe.

Supporting paragraphs: Suwałki Region Lithuania–Poland border
Answer: Lithuania–Poland border