Hamburg: For days, protesters seethed. They marched. They chanted. They took over public parks. They refused to obey police commands to disperse. They filled this northern German port city with signs condemning global trade as world leaders descended for the G20 economic summit.

Then, late on Friday, violence erupted as far-left militants ravaged parts of Hamburg, setting cars on fire, smashing store windows and looting.

The turmoil created difficult questions for activists who continued to rally on Saturday as some made a point of disavowing radical tactics. It also renewed concerns about whether Hamburg - whose more than 1.7 million residents make it the second-largest city in Germany, a country with federal elections several months away - was a wise location for a summit bringing together many divisive heads of state. All together, all at once, in a moment of global unease, were President Donald Trump, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan.

Antipathy toward Trump was a particular rallying point in demonstrations that otherwise lacked a unifying theme. Protesters railed variously against capitalism, climate change and national borders, among many other grievances.