In less than three weeks, Russia’s invasion of Ukraine has sent 3 million people fleeing their homes to neighboring countries — with still millions more displaced domestically — in what has quickly become Europe’s worst migrant crisis since World War II.

While the majority have been compassionately welcomed by host countries rejecting President Vladimir Putin’s indiscriminate attack, the sudden influx of people is having a profound impact on the European landscape — with potentially significant consequences.

Nowhere is that impact more pronounced than in Poland.

Since the start of the war on Feb. 24, Poland has welcomed over 1.8 million refugees — almost twice the 1 million authorities had anticipated and increasing its population by 4.8%.

The east European country is a natural point of entry for Ukrainians owing to their 530-kilometer shared land border, as well as numerous historical, cultural and economic ties. Indeed, there is already a sizeable Ukrainian diaspora in Poland following an earlier spate of migration after Russia’s 2014 annexation of Crimea.

But as the number of refugees requiring humanitarian assistance spirals well beyond initial estimates, it is putting considerable strain on the government and the dozens of relief agencies that have mobilized to help them.

“First, all of the people knew where they wanted to go. They had some friends they wanted to stay with [in Poland],” said Dominika Chylewska, head of communications at Caritas Polska, a charity offering relief to migrants at Polish reception points including Przemysl, a city 12 kilometers from Ukraine’s border.

Others still planned to travel further afield to Berlin, Prague and Tallinn, she said.

“Now, we already see that there are more people coming without any final destination,” said Chylewska.

That raises questions about the long-term fate of those migrants and what more the European Union will do to support host countries like Poland.

“It puts the EU in a bind,” said Adriano Bosoni, director of analysis at intelligence firm RANE, highlighting decisions the bloc will face around financial aid and permanent residency.

So far, the EU has assigned 500 million euros ($547 million) for humanitarian aid to Ukraine. Yet estimates from the Economist Intelligence Unit suggest that the cost of supporting 5 million refugees could be 50 billion euros in 2022 alone.

Meantime, the bloc has activated a never-before used Temporary Protection Directive granting Ukrainian nationals the right to live and work in host countries for up to three years.

Longer term, however, it will have to decide if it will offer permanent asylum to migrants, and how it might redistribute them across the bloc to ease the burden on primary hosts like Poland, Hungary, Slovakia, Romania and Moldova.

“The [Polish] government will not be able to cope with the crisis without extensive assistance from the EU. This includes both financial assistance and resettlements of refugees,” said Alessandro Cugnasca, country risk service manager at the EIU.

Even before the crisis, Poland, a country of almost 38 million, was undergoing a demographic shift.

In the years since joining the EU in 2004, the Eastern European nation has experienced high levels of emigration as skilled workers have headed west to other member states, seeking higher wages and increased opportunities.

Meanwhile, a falling fertility rate — driven, like many of its Western peers, by greater sex education, higher female workforce participation, and increased urbanization — has added to the country’s overall population decline.

That could make Poland — already one of Europe’s fastest growing economies before Covid — a grateful recipient of long-term, skilled workers, said Bosoni.

“Importing millions of young Ukrainian workers who can join your workforce and contribute makes sense from an economic point of view,” he said, citing the high education level of migrants, mostly women and children, from Ukraine.

But still, the political risks for Poland and its neighbors are notable.

Migration can be a political hot potato, with the 2015 Europe migrant crisis thought to have bolstered far-right movements that swelled across the continent in the years that followed. At that time, Poland was reluctant in accepting migrants, largely from Syria and North Africa — a fact that has not gone unnoticed in its response to Ukraine.

“Polish citizens remain very supportive of Ukrainian refugees. But the crisis has the potential to cause political instability over the medium term,” noted EIU’s Cugnasca.

“War refugees, unlike labor migrants, will require significant financial support from the state and this could lead to a political backlash down the road,” he added, pointing to Poland’s next parliamentary election due in 2023.

Of course, the longer term implications will depend largely on the outcome of the conflict, analysts agreed.

If, as many fear, Russia succeeds in its invasion and installs a pro-Kremlin government, the likelihood of migrants returning home is far lower.

But if, as Western allies hope, there is a resolution to the conflict that restores a sovereign Ukraine, the majority of migrants may choose to return home and embark on the lengthy task of rebuilding their war-torn country.

“Most who left would like to be able to go back,” said Bosoni. “They are not economic migrants, they are people escaping war and death.”