WARSAW, Poland (AP) – Poland is deploying thousands of troops to its border with Belarus, calling it a deterrent move as tensions between the two neighbors ratchet up. Those tensions between Poland—a NATO and European Union country—and Belarus, which is Russia’s ally in its war on Ukraine, have been building up in recent months on the border. Here is why.

Origins of the Tensions

Poland has been backing the Belarusian opposition ever since the 2020 presidential elections, where pro-Russian Belarusian leader Alexander Lukashenko won a sixth term in a vote that Poland and the wider Western community saw as rigged.

In 2021, Belarus began organizing and pushing thousands of migrants from the Middle East and Africa across the border into Poland. The move is seen by Poland and the EU as planned with the Kremlin and intended to cause instability in Europe. Poland’s right-wing government, hostile to the idea of accepting migrants, built a $400,000 wall that substantially reduced the inflow.

After Russia’s February 24, 2022, invasion of Ukraine, Poland condemned the attack and has been supporting Kyiv with military equipment, political backing and humanitarian aid, including hosting more than 1.2 million refugees. Belarus is on Russia’s side in the conflict, and Poland is participating in international economic sanctions on both countries.

Recent Actions by Belarus and Russia

Belarusian state officials and pro-government activists have formed a group called the Patriotic Force Command, which Minsk uses as a political tool. In a recent address to the Polish nation, the group alleged that Polish politicians are “igniting the fire of war with their actions and rhetoric” and are being “driven by the frenzy of chauvinism.”

Meanwhile, officials in Moscow have repeatedly voiced groundless allegations that Poland intends on annexing western regions of Ukraine. Moscow also says it has moved some of its short-range nuclear weapons into Belarus, close to the NATO eastern frontier.

Poland is also concerned over the presence in Belarus of thousands of Russian Wagner mercenaries who were recently said to have taken part in training near the border. Two Russian men were arrested last week in Poland accused of having spread the Wagner group’s ideology. More than half of Poles questioned recently by the IBRIS survey center said they considered the Russian mercenaries in Belarus as a threat.

Two Belarusian military helicopters flew at low altitude over the Polish village of Bialowieza near the border for a few minutes last week before returning to Belarus, an action that Poland said was a provocation.

Why Is the Region So Strategically Important?

Beside being NATO’s and the EU’s frontier, Poland’s eastern border includes a strategic spot, the so-called Suwalki Gap—60 miles of border with Lithuania that links the three Baltic states, Lithuania, Latvia and Estonia, to the rest of the NATO alliance and the EU. The narrow gap also separates Belarus from Kaliningrad, a heavily militarized Russian exclave that has no land connection to Russia.

Military analysts in the West have long viewed the Suwalki Gap as a potential flashpoint in any confrontation between Russia and NATO. They worry that Russia might try to seize the gap and cut off the three Baltic states.

The area is heavily protected by Polish and U.S. troops on the Polish side and Canadian and German troops on the Lithuanian side.

Poland Is Beefing Up the Border

Poland’s government says it will not be intimidated and is building up its defense and deterrence potential and moving troops and modern equipment east, to beef up the border with Belarus and with Kaliningrad.

“There is no doubt that the Belarus regime is cooperating with the Kremlin and that this action is aimed against Poland in order to destabilize our country,” Poland’s defense minister, Mariusz Blaszczak, said last week.

Poland increased its spending on defense to more than 2.5 percent of GDP last year and the amount is to rise again this year. It spent more than $16 billion on weapons, including Abrams tanks, Patriot missile systems, jet fighters, tanks and howitzers. Some of them will replace Soviet and Russian-made equipment offered to Ukraine.

Poland’s Election Adds to the Military Defense Drive

Poland is to hold crucial parliamentary elections on October 15. The populist Law and Justice party, which has been in power since 2015, is intent on winning an unprecedented third term.

The party is tapping into the public’s security concerns and stressing its efforts to beef up defense, seeking to rally voters around its policies and discredit the opposition and its main leader, former prime minister Donald Tusk.