The refugee wave arriving in Lithuania is bound to qualify as some of the year’s most peculiar news. Refugee waves are ordinarily the tragic outcome of conflicts, but Belarus’s president, Alexander Lukashenko, has taken to deliberately sending migrants across the border to Lithuania, forcing it to build a border barrier. Lukashenko is demonstrating that in the grey zone between war and peace, cynicism and innovation are a powerful combination.

On refugee matters, the playbook usually goes something like this: large numbers of people from conflict zones arrive in Italy and Greece. Italy and Greece ask European allies to help, but many are reluctant, especially if they’re asked to receive some of the new arrivals. Indeed, some central European countries have so fiercely opposed mandatory refugee quotas that last year the European Commission abandoned its plans to impose them.

Now, a rather different refugee wave is taking place in Lithuania. During the first seven days of July, 779 illegal migrants crossed the Belarus-Lithuania border. Compare that to last year, when a total of 81 illegal Belarusian migrants were detained by Lithuanian border guards.

The influx is the result of Lukashenko delivering on a sinister promise, made at the end of May, to flood the EU with migrants and drugs. He made the threat in response to the EU’s ban on flights traversing Belarusian airspace. Lithuania had unsurprisingly pushed for such a ban after a Vilnius-bound Ryanair flight from Athens carrying opposition journalist Roman Protasevich was diverted over Belarusian airspace on 23 May and forced to land in Minsk, where Protasevich was arrested.

If Lithuania had done nothing, it would not be facing a wave of illegal migrants, most of whom say they’re from Iraq and many of whom seem to have arrived in Belarus on special flights from Baghdad. It wouldn’t have to build the border barrier it’s now erecting. But by doing nothing, it would also have sent the message to Belarus that it’s OK to divert commercial airliners carrying, say, Belarusian opposition activists. Many such activists, including Lukashenko’s opponent in last year’s presidential election, Svetlana Tikhanovskaya, have been given refuge in Lithuania. And by doing nothing, Lithuania, the EU and the UK – who all banned inbound and outbound flights from using Belarusian airspace – would have signalled that government-sponsored aviation piracy is acceptable. Instead Lithuania took a stand and is being punished for it.

But here’s the challenge in the grey zone between war and peace: if the targeted country responds to one aggressive act, the aggressor gets an opportunity to attack once again. That leaves Lithuania struggling with an astonishing border-crossing surge. The migrants, in turn, must be wondering what sort of geopolitical game has brought them to this unexpected part of the world. Now Lithuania will have to spend precious taxpayer money building the border barrier, but doing so may simply entice Lukashenko to try yet another dirty trick. Brace yourself for another performance in response to Lithuania’s decision, earlier this month, to grant Belarus’s opposition official diplomatic status. What might the Belarusian leader think up? The beauty of aggression in the grey zone is that the attacker has the advantage and is limited only by his or her imagination.

Pity the Lithuanians, who face a tough summer dominated by Belarus and a heatwave that is seeing temperatures above 30 degrees Celsius even in the evenings. But congratulate them, too, on standing firm even when there’s a price to pay. That means that Lukashenko, once he’s completed this round of aggression, is likely to leave Lithuania in peace. In fact, he may decide to instead test the rest of us. Sure, he can’t easily flood, say, Sweden or the UK with illegal migrants, but there are lots of other devious acts he could try. (In case his staff is reading, I won’t provide him with suggestions here.)

Grey zone aggression works like schoolyard bullying: ducking is not a sustainable strategy. When China suspended imports of Norwegian fish after the Norwegian Nobel Prize Committee awarded the 2010 Peace Prize to the Chinese dissident Liu Xiaobo, other governments said nothing, hoping that their countries wouldn’t be similarly punished. Instead China has bullied many more countries, but they haven’t dared to team up and respond. Belarus isn’t China, but no wonder Lukashenko is emboldened. Congratulations, Lithuania, for not backing down.

Elisabeth Braw is a Visiting Fellow at the American Enterprise Institute (AEI), where she focuses on deterrence against emerging forms of aggression, such as hybrid and grey zone threats.