But the world in 2019 looks very different to how it did in 1949. NATO has been slow to adapt to a changing world, and the leaders assembling in London know it. The alliance was conceived as a defense against Russian military force, but the rise of China has shifted the balance. It matured as a forum for military cooperation and coordination, but President Donald Trump has often acted unilaterally — for instance withdrawing U.S. troops from Syria in October without consulting NATO allies.