Here is one example, happening now, of a deliberate attempt to harm a country by flooding it with illegal migrants. It is no secret that a flood of illegal immigrants is harmful to a country, and malevolent actors will make deliberate attempts to harm a country by flooding it it with such

Belarus–European Union border crisis

From Wikipedia, the free encyclopedia

The Belarus–European Union border crisis is a migrant crisis consisting of an influx of coordinated groups of immigrants, primarily from Iraq, with smaller groups hailing from elsewhere in the Middle East and from North Africa,[21][22] to Poland, Lithuania and Latvia via those countries’ borders with Belarus. . . .

The crisis began sometime around July 7, 2021, when Belarus’s dictator Alexander Lukashenko threatened to “flood” the EU with “drugs and migrants”.[23] Later, Belarusian authorities and state-controlled tourist enterprises, together with some airlines operating in the Middle East, started advertising tours to Belarus and fraudulently promoting opportunities of a trouble-free entry into the European Union’s territory for the prospective migrants all over social media groups.

Those who arrived in Belarus, most of whom were trying to reach Germany, were then given instructions about how and where to trespass across the EU’s border, and what to tell the border guards on the other side of it. Migrants said that Belarus provided them with wire cutters and axes to cut through border barriers and enter the EU;[24]

And here is Poland’s response (Water cannons, not fist bumps and free cellphones)