The spotlight is back on NATO as alliance leaders prepare for one of the most consequential summits in recent memory. Turkey is all set to host the upcoming NATO summit from July 7. But behind the carefully choreographed family photos lies an uncomfortable reality. Relations between the US and several of its closest allies are under strain. From defence spending and trade disputes to Ukraine and questions over America's long-term commitment to European security, old fault lines are widening. NDTV World's Gaurie Dwivedi explains what's behind the US-NATO rift.