The conflict in Syria becomes more complex every day that it continues, and the country’s prospects have gotten only worse. The daily horrors that Aleppo’s besieged citizens are now experiencing mark a new low point, following the collapse of the latest ceasefire, brokered by the United States and Russia, which disturbingly fell apart precisely at the same time that world leaders were gathered together for the United Nations General Assembly.

When the Syrian conflict finally ends, three of its defining features will complicate reconstruction efforts. For starters, parties on all sides of the fight have disregarded international human rights law and violated basic humanitarian norms. In fact, blocking humanitarian aid, attacking civilians, and targeting sites specially protected by international law have become strategies of war.

Just since April, Syrian hospitals have suffered dozens of attacks, and aid has been withheld from some of the most devastated villages. Many hospitals in Aleppo have had to close after being targeted during the siege.

These actions may constitute war crimes, and they are sadly not new. In 2015 alone, medical installations in Syria affiliated with Doctors Without Borders incurred 94 attacks, leaving 23 of the organization’s workers dead and another 58 wounded. Last May, the U.N. Security Council adopted a resolution calling for all parties involved in Syria to respect international humanitarian law; now, Security Council members are accusing one another other of violating their own resolution.

A second dynamic that could frustrate any peace effort is the conflict’s complex map of players, all of which will have to be accounted for in a final accord. While this map has changed significantly since the war began, the level of fragmentation within the groups on either side has become increasingly evident lately. Now that the jihadist group Nusra Front has changed its name to Jabhat Fatah al-Sham and reportedly dissociated itself from Al-Qaeda, it is better positioned to ally with other rebel factions that have also rejected Al-Qaeda.

But while this rapprochement strengthens the fighting groups militarily, it also blurs the lines between rebels and Islamist radicals. This has occurred while rebel groups not closely aligned with Nusra have become weaker, allowing the Syrian regime to insist that it is not suppressing a rebellion, but fighting a war against terrorism. Thus, at the U.N. General Assembly, Syrian Foreign Minister Walid al-Moallem recently accused the U.S.-led coalition in Syria of abetting terrorist organizations, including Daesh (ISIS).

Some months ago, discussions about a peace process centered on the question of whether Assad should go immediately, or remain during a transitional government; now, the question is whether the former Nusra is a viable partner.

But the pro-Assad side has divisions of its own. In addition to the Russian army, Syrian, Iraqi, Iranian and Afghan groups are also fighting for the regime, and each of these actors has its own interests.

Some parties’ interests in the war are well known: Assad wants to remain in power; Russia wants to demonstrate its status as a great power capable of resisting the U.S.; and Iran wants to increase its regional influence and secure access to the Mediterranean. When the fighting ends, these positions will only become more entrenched.

A third obstacle in the path toward Syrian peace is the U.S.-Russia stalemate. After so many broken cease-fires, the two countries clearly lack mutual trust. And as Dmitri Trenin of the Carnegie Moscow Center has pointed out, the latest failure could have far more worrying consequences than past diplomatic impasses.

So far, the U.S. and Russia have not only broken off bilateral negotiations; mutual nuclear agreements have also come under threat. After the U.S. accused Russia of committing war crimes in Syria, Russia declared that it was suspending an agreement to dispose of surplus plutonium unless the U.S. meets certain conditions, including compensating Russia for the costs of Western sanctions imposed after Russia annexed Crimea in March 2014.

For its part, the U.S. is in an uncertain position now that rebel factions have regrouped and its direct cooperation with Russia is on hold. President Barack Obama has only a short time left in office, which makes any major foreign-policy shift under his administration almost impossible. As the battle for Aleppo rages on, so, too, does the U.S. presidential election campaign that will determine his successor.

After more than five years of conflict in Syria, retreating without having found a solution is not an option. Although the new map of players complicates things, there is no doubt that they must all participate in a peace deal; otherwise, any agreement will prove ephemeral. Likewise, in order to rebuild Syrian civil society for the long term, all of the warring parties will have to take responsibility for their crimes.

The issue of responsibility will be one of the most difficult challenges in the effort to achieve lasting peace. We will need committed leaders both inside and outside Syria. Although the U.S. presidential election will be consequential, it has also become clear that peace cannot be delivered by the U.S. and Russia on their own.

European leaders should step in to restart negotiations. The European Union has mistakenly sat on the sidelines of these talks for too long, despite Syria’s importance to its own security and interests, and despite its responsibility to Syria’s citizens. The EU should make every diplomatic and humanitarian effort to bring together all participating parties and end the violence as soon as possible. Only then can Syria’s reconstruction begin.