The "Battle of Seattle" in 1999 marked the unofficial start of the anti-globalization movement. Organizing under the radar, this new protest movement burst onto the scene with tens of thousands taking to the streets - and shutting the city down. Protesters criticized the World Trade Organization (WTO) as promoting a "race to the bottom" in terms of environmental, human rights and labor standards.

The Seattle actions brought together a broad coalition, with rank-and-file labor unionists marching arm-in-arm with environmentalists. Previously at odds over jobs, the two factions now faced a common enemy: corporate dominance and the unchecked quest for corporate profit. International financial institutions promoting free trade became the symbols - and targets - of this broad new movement.

"Think globally, act locally" is one of the slogans of the anti-globalization movement. Demonstrators organized protests as street parties in response to a crackdown from authorities and made calls to decentralize and globalize. As the G8 met in Cologne in June 1999, "J18" protests also took place in London and Eugene, Oregon. The emphasis on having fun drew many young people into the movement.

In 2001, thousands protested the G8 under the slogan "another world is possible." This alternative vision was against environmental destruction and the growing gap between rich and poor. Indeed, a criticism of the anti-globalization movement was that it was against so much - but what was it for? Protests in Genoa were marked by clashes between security forces and increasingly militant protesters.

As many as 20,000 policemen sought to keep the demonstrations under control - in vain. The legacy of Genoa included innumerable injuries, and even one fatality: Police shot dead the Italian Carlo Giuliani in a street battle. For years afterward, such summits were held in increasingly remote - and defendable - locations. For the protesters, this symbolized how they served - above all - the elite.

In 2001, the WTO met in Doha - for protesters, hard to reach - and with Qatar not exactly known to vaunt free speech. Was the era of mass anti-globalization demonstrations over? Doha's slick and elite image added fuel to the accusation that such institutions were insulating themselves against popular movements.

The G20 summit in Toronto in 2010 went down in history - as the scene of Canada's largest mass arrest. Police cracked down violently on demonstrators, arresting more than a thousand people - who were mostly later release without charge. The mass false arrests here had followed similar actions: in Washington at IMF/ World Bank protests in 2002, and at the FTAA protest in Miami in 2003.

In 2015, the G7 meeting at Schloss Elmau in Bavaria - likewise a remote and defendable location - took up a number of environmental topics, such as threats to the world's oceans. G7 countries vowed to more effectively and intensively work on fighting waste in the seas. Environmental topics appeared to have broken through to agendas that previously had been dominated by economic ones.

For the G20 to set its 2017 meeting in the major metropolis of Hamburg could be seen as a reconciliation. Currently in the rotating presidency of the G20, Germany has been praised by civil society groups for its attempts to engage, such as here at the "Civil20" meeting in June. Climate change is at the top of Germany's G20 agenda - reflecting increasing concern over the issue worldwide.

In Hamburg, urban camping should reduce the environmental footprint of protesters - although a conflict over whether to allow such camping within the city has been a bone of contention. Again, 20,000 police will attempt to keep order during the summit. An atmosphere similar to that of a summer music festival is tempered with serious undertones as protests get underway.

As the most polluting fossil fuel, coal is a clear target. Greenpeace activists pulled alongside the Chinese coal freighter "Golden Opportunity" in Hamburg's port to point out Germany's hypocritical position on the topic. Similar actions are surely to come - learning from the anti-globalization movement, the climate justice movement has built a broad coalition. It's not just eco-freaks anymore!