"For years, we have heard warnings that Europe needs to contribute more to NATO's capability"

This quote by Lord Robertson is describing the requirement for European nations to contribute more to the North Atlantic Treaty Organization (NATO). For many years, NATO has been warning European countries that they need to increase their contributions to the organization in order to keep its capability. This is particularly crucial in light of the altering security environment in Europe, with the rise of Russia and other threats. NATO is a collective defense company, and it is necessary that all members contribute their fair share in order to guarantee its effectiveness. Lord Robertson's quote is a pointer that Europe requires to step up and take obligation for its own security, and that it can not depend on the United States to do everything.