Speaking at a campaign event in Bavaria, Ms Merkel emphasised the need for friendly relations with the US, Britain and Russia, but added: "We Europeans must really take our destiny into our own hands."
She said that, as the traditional western alliance is threatened by the new US presidency and Brexit, "the times in which we can fully count on others are somewhat over, as I have experienced in the past few days."
While Germany and Europe would strive to maintain relations with America and Britain, Ms Merkel said Europeans "have to fight for our own destiny".
Donald Trump says Nato member states need to 'pay up'
Her comments came after Mr Trump said he needed more time to decide if the US would continue backing the Paris climate deal, which has frustrated European diplomats.
Mr Trump, who has previously called global warming a hoax, came under concerted pressure from the other leaders to honour the 2015 Paris Agreement on curbing carbon emissions.
Although he tweeted to say he would make a decision next week, his apparent reluctance to embrace the first legally binding global climate change deal, signed by 195 countries, clearly annoyed Ms Merkel.
“Understanding this process, the heads of state and of government of Canada, France, Germany, Italy, Japan and the United Kingdom and the presidents of the European Council and of the European Commission reaffirm their strong commitment to swiftly implement the Paris Agreement."
A source who has been in contact with people involved in the decision told Reuters a couple of meetings were planned with chief executives of energy companies and big corporations and others about the climate agreement ahead of Mr Trump's expected announcement later in the week.