Hardly is Angela Merkel's vacation over, and fresh headaches are approaching. She began the late summer with an urgent trip to Spain on Saturday, when she attempted to start picking at the tightest and most complicated of Gordian knots — how to regulate migration in Europe. Prime Minister Pedro Sanchez had already become the one of the first European leaders to reach a new bilateral migration deal with Germany, which means Berlin will be able to send a few refugees back to Spain if they have already registered there.

The most profound byproduct of that agreement, and the deals that Merkel's administration will be trying to strike in the coming weeks, is that Germany has been forced to admit the Dublin system is no longer functioning.

Spain is now one of Germany's most vital allies in Europe

Read more: What you need to know: the German-Spanish migration deal

Migration: The eternal problem

The Dublin agreement, first put together in the 1990s, is meant to determine which European Union state is responsible for asylum applications, but in practice it often means that applications are not properly heard, potentially violating migrants' rights. The Dublin procedure almost descended into chaos in 2015 and 2016, when it had to be partially suspended as a result of the bureaucratic crisis triggered by an influx of refugees into Europe from Syria.

Whatever solution Merkel finds, it will likely be incremental — though with European Parliament elections approaching next year, she and other EU leaders will be hoping for tangible results sooner rather than later.

Spain, along with France, is one of the few major non-populist governments left in Europe, making it a vital ally for Germany. That dwindling group faces a showdown with the more right-wing governments on September 20, when Austria is hosting an informal EU summit.

Austria, which currently holds the presidency of the Council of the European Union, is one of the countries pursuing an increasingly draconian migration policy, and for Merkel and Sanchez, the summit could become a dragon's den scenario: They will have to defend a new cooperative deal with so-called countries of origin and transit, such as Morocco and Libya, who are demanding more help from the EU to prevent migrants coming to Europe.

Given the confrontational mood in Europe, it seems unlikely that the suffering of the migrants in North Africa will be high on the agenda. The Moroccan human rights organization AMDH has reported that the government there had recently destroyed camps near the Spanish enclave of Melilla and bused several hundred migrants, mainly from sub-Saharan Africa, back to the country's interior.

Read more: Nord Stream 2 - what is the controversy about?

Russian questions

Another eternal problem with some immediate meetings ahead will be how to deal with Russia. It was announced on Monday that President Vladimir Putin would be visiting Germany on Saturday, where the two leaders will sit down together at the government's retreat in Meseberg, outside Berlin, just three months after Merkel met Putin in the Russian beach resort of Sochi.

As for what they should discuss, it could prove difficult for the two long-serving leaders to know where to start: Russia and Germany are facing any number of intractable differences, most notably over the conflicts in Syria and Ukraine.

Along with France, Germany has been trying to mediate between the Ukrainian government and the pro-Russian separatists who currently control the country's eastern regions. The United Nations has also been trying to broker a ceasefire in the slow-burning conflict, which has claimed at least 10,000 lives since it began in November 2013, though the negotiations over how the body would police the deal remains a problem.

The Syrian war, meanwhile, will be the subject of another summit on September 7, hosted by President Recep Tayyip Erdogan of Turkey, which France and Russia will also attend. Putin, who remains Syrian President Bashar Assad's closest ally among major powers, is likely to be a key figure.

Another thorny German-Russian issue is the Nord Stream 2 pipeline — a 1,200-kilometer (750-mile) infrastructure project which Russia wants to use to sell gas to Germany. US President Donald Trump brought up the project at the recent NATO summit in Brussels, complaining on Twitter that it wasn't fair for Germany to be protected by US troops while it was doing economic deals with Russia. It was left to NATO Secretary General Jens Stoltenberg to point out that the alliance had always separated economic agreements from security questions.