The incursion by Russian drones over Poland that prompted NATO forces to launch warplanes overnight is the latest of several cases since Moscow launched its full-scale invasion of Ukraine in 2022 in which the airspace of European countries near the Ukrainian border has been violated.

Violations of airspace are particularly sensitive in NATO countries like Poland.

The latest incursions there came during a large-scale Russian drone attack on Ukraine, and it remained unclear if they were intentional. Belarus, a Russian ally, issued a statement that framed the episode — without providing evidence — as an accident.

Still, any violation of a NATO country’s airspace raises fears that the conflict could spread and trigger a response by the alliance.

In some past cases, what landed in countries neighboring Ukraine was believed to be debris from Russian drones or missiles that were shot down. And in one case, a Ukrainian air-defense missile likely went astray as it tried to fight off a Russian attack.

Here are some past incidents:

Poland

In November 2022, in one of the incidents that caused the most alarm, Poland said that an explosion that killed two people near the Ukrainian border had “most likely” been caused by a Russian-made missile. But nearly a year later, a Polish investigation found that the deaths had, in fact, most likely been caused by a Ukrainian air-defense missile that had misfired while attempting to shoot down a Russian missile over Ukraine. However, the Polish government and NATO said that Russia was ultimately to blame because of its war in Ukraine.