Last week, the heads of state and government of the European Union opened the door to Ukraine, Moldova and Georgia eventually becoming members of the E.U. They unanimously followed the recommendation of the European Commission — the E.U.’s executive body — which had said that Ukraine and Moldova should be declared “candidates” for membership, and offered Georgia the possibility of becoming a member if it fulfills certain conditions.

This is a big reversal of E.U. policy, but it doesn’t mean that these countries will become members any time soon, or perhaps at all. Here is what you need to know.

The E.U. had little choice but to open the door

In 2014, the E.U. offered Ukraine, Moldova and Georgia “association agreements” that covered free trade, cooperation and integration into the E.U.’s market arrangements. However, the E.U. pointedly didn’t make any commitments about candidacy or membership, although Ukraine, Moldova and Georgia interpreted the agreements as a steppingstone toward membership.

The E.U. has always been reluctant to offer membership to comparatively poor European countries with weak bureaucracies and less-stellar records on democracy and the rule of law. Created as a union of democratic nations, the E.U. depends on the ability of its members to effectively implement its rules in their own economies.

If Ukraine, Moldova and Georgia become full members, they will want money from the E.U. budget, pulling resources that would otherwise go to other poor member states. Some of their citizens will move to other E.U. countries — they would have the right to do so, under the E.U.’s rules. That may make some member states unhappy.

So why have the E.U.’s existing members voted to open the door to these countries, given that some of them might have self-interested reasons to prefer to keep them out? My research on previous debates over bringing new members in suggests that moral exhortations can combine with what I call “rhetorical entrapment” (how politicians’ rhetoric can make them do things they may not want to do) to overcome resistance from existing members.

In the early 1990s, the democratic transition and the “return to Europe” of countries that had been part of the Soviet Union’s “Warsaw Pact” made it hard for existing E.U. members to block them from joining. After all, the E.U. was supposed to work toward democratically unifying the continent. When Turkey democratized in the early 2000s, skeptical E.U. members found it similarly difficult to publicly express their opposition.

That helps explain what’s going on now. Since the Russian invasion in February, the Ukrainian leadership and their E.U. supporters have argued that Ukraine’s heroic resistance not only demonstrates the country’s profound European identity but also defends European ideals of free association against Russian efforts to revise borders through military force.

All three countries understood that the crisis provided an opportunity. Ukraine had submitted its membership application just four days after the start of the Russian invasion and was quickly followed by Moldova and Georgia. Most E.U. members were initially skeptical, or suggested alternatives to enlargement, but they were morally unable to explicitly oppose these countries’ applications.

Candidacy is not a commitment to full membership

The E.U.’s new decision is largely symbolic and may be reversed. Becoming a full member is a long and complicated process fraught with obstacles. The three countries need to meet additional political conditions — including judicial upgrades, anti-corruption measures and curbing the influence of oligarchs — to start actual negotiations on accession, in Moldova and Ukraine’s cases, and for Georgia to gain candidate status.

Every year, the commission will evaluate each country’s progress. Each individual member can veto any further step in the membership process, including the beginning of negotiations, progress through different specific topics and the final signing and ratifying of the treaties that would allow a candidate to become a full member.

In short, candidacy is just one step on a long road. North Macedonia has been a candidate since 2005, but first Greece and then Bulgaria vetoed the opening of negotiations for nationalist reasons. Negotiations with Serbia and Montenegro have stumbled along for the past 10 years, and those with Turkey were half-blocked in 2007 and completely stalled after Turkey’s 2016 coup.

Past evidence suggests that the conditional offer of membership can help candidate countries to shore up democracy and institute policy updates. The E.U. may be better able to deeply “Europeanize” Ukraine, Moldova and Georgia, but only if the candidate countries are run by democratic and Western-oriented governments. Authoritarian nationalist regimes in Turkey and Serbia have been unwilling to make concessions that might undermine their control.

Furthermore, the E.U.’s ability to impose conditions on candidate countries has paradoxically weakened as it has made the conditions harsher. The E.U. wants more rigorous conditions, because it worries that previous countries it has let in have weak rule of law. It will be very difficult for current candidates (which are starting from a worse situation) to ever meet the requirements.

And public opinion — which was mostly indifferent to new E.U. member states — has become divided since the mid-2000s. Populist fringe parties have been able to mobilize popular skepticism, so that a 2016 no vote in a Dutch referendum delayed the entry into force of Ukraine’s association agreement with the E.U. Other member governments have vowed to put future accession treaties to a referendum, too. These political uncertainties make candidate governments less willing to implement costly policy changes.

Now that the war is highly visible, and accession a dim future possibility, surveys show that a solid majority of citizens in almost all member states support Ukrainian membership. That majority may shrink when the costs of accession become more visible. These uncertainties, in turn, may push the E.U. to offer the candidate countries tangible intermediate steps of integration to reward their efforts if it wants to keep the process alive.