[Video transcript]
By the early 1950s, the most violent period in modern European history was coming to an end, and the wars and conflicts that had long plagued the continent were giving way to what would become decades of relative peace and, with it, disarmarment.
Looking at this chart, you can see how military budgets in Europe decreased over the years.
Spending averaged 4 percent of GDP by the start of the1960s. It gradually declined to below 2 percent where it has hovered ever since.
But reality has changed. And Europe is preparing to fend for itself, alone.
Ursula von der Leyen, EU Commission President: "I do not need to describe the grave nature of the threats that we face. The real question in front of us is whether Europe is prepared to act as decisively as the situation dictates. The answer from European capitals has been as resounding as it is clear. We are in an era of rearmament."
EU leaders have made big pledges to ramp up defence investments, amounting to hundreds of billions of euros.
But how will this be paid for, and how did past European governments fund their defense budget increases?
Christine Mhundwa, DW correspondent: "The Kiel Institute for the World Economy looked at data going back 150 years and it showed that past military build ups in Europe were financed through a mixture of increased taxes and borrowing and governments hardly made cuts to social spending. The bigger the build up, the more dominant debt was."
Governments appear to be moving in step with history by taking on more debt.
Rules governing borrowing are being relaxed in Brussels and in major capitals like Berlin, where the parliament took the historic decision to change the constitution so the government could borrow more.
But many European governments are heavily indebted already, so there will be trade-offs for the increased debt and these include raising taxes and capping social spending.
Pierre Jaillet, economist, Jacques Delors Institute: "You cannot keep or maintain all the expenditure, increase your military spending and keep your public debt on a sustainable trajectory, you really have choices to make the problem is that making choices is politically difficult especially when it concerns social expenditure. Reducing public spending, making sacrifices is politically touchy and that's the reason why the politicians so far are not ready to do it."
Because there are warnings that cuts to social spending and public services could be a political disaster — by driving more citizens towards far-right political forces.
Europe's leaders say rearming is essential because of the threat to security from Russia, and the threat of being abandoned by the US.