Former US Secretary of State John Kerry spoke on Friday at the Munich Security Conference about the importance of international cooperation in meeting world challenges.

Kerry, Barack Obama's top diplomat from 2013 to 2017 and also the defeated presidential candidate of 2004, accused US President Donald Trump of inaction in addressing global issues such as climate change and defense spending.

"The president of the US is the most powerful position in the world ... but it requires the execution of that power and it hasn’t been happening …" Kerry said while speaking to DW's Editor-in-Chief Ines Pohl. "Trump has been breaking apart NATO, pushing people away, insulting Angela Merkel, insulting leaders in Europe and praising people like Putin … that's unacceptable."

Read more: Afghan peace deal 'closer than ever'

Germany's role in the world stage

Kerry said the European Union plays an even more important role post-Brexit, adding that Germany particularly "is an incredibly important country." 

"For years now, Germany, Great Britain and France shared major responsibilities with the 28 nations in the effort to try and move in the same directions," Kerry said. However, he also said Britain's departure had strengthened resolve among the other 27 EU members, both to increase their cooperation and to fix some of the problems that helped drive the Brexit vote.

"I think Europe in many ways is stronger for this, but we have to now deal with real problems," Kerry said. "People need to see that globalization doesn't mean exploitation, people need to see that their wages go up if they work harder and produce more. The upper 1% of our country has been getting more than 51% of the income that is earned, broadly. That's not sustainable."

Climate inaction

Kerry said that Trump had been ducking both the local and global challenges of climate change.

"To have a president who wants to put his head in the sand and pretend it's not happening is a moment of enormous irresponsibility," he said. "President Trump is lying when he says it [climate change] is a lie."

Kerry said Trump's denials of the world's climate problems were purely for political and ideological reasons, and called on the president to organize an emergency G20 climate meeting.

Peace in Afghanistan

When asked about the US troop withdrawal from Afghanistan and what it means for peace in the country, Kerry said the Taliban must "be persuaded to accept terms which do not predicate the end of the existing government," adding that a "sufficient platform" must be established so that if there was Taliban retaliation, "there is an immediate ability to be able to stop them [the Taliban] from having a military solution."

Kerry also called on China and Russia to become "guarantors" in the Afghanistan peace process, but acknowledged that it would require "creative diplomacy."

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