NATO leaders will seek reassurance on Monday from U.S. President Joe Biden that after four years of denigration by his predecessor Donald Trump, the alliance can count on the support of the United States, its most powerful member. In a more pared-back gathering than past NATO summits in part due to COVID-19 restrictions, without fighter jet fly-pasts, the 30 allies will gather in their glass and steel headquarters to agree reforms for a multipolar, post-Cold War world where China"s military rise presents a new challenge. The summit is a "unique opportunity" to renew transatlantic ties, according to NATO Secretary-General Jens Stoltenberg. Brussels" town hall in the historic Grand Place will be illuminated in NATO"s signature blue on Sunday night while the Belgian capital"s famed bronze fountain of a boy urinating will also don a NATO-branded outfit on Monday. "The first thing is for Biden to recommit to NATO"s collective defence," Jamie Shea, a former senior NATO official who was at a 2018 summit at which Trump considered quitting the alliance. Trump brought a television reality-show quality to the NATO summits he attended from 2017 to 2019, diplomats said, attracting international attention but also wearing down allies whom he called "delinquent" for not spending enough on defence. Biden has already annulled a Trump decision to pull U.S. troops out of Germany, although there is still American pressurefor European allies to pay more towards their own security. Stoltenberg said on Friday that European allies, Turkey and Canada will have collectively increased their defence budgets by $260 billion by the end of 2021, compared to 2014. "This summit with Biden should be a signal to the world that NATO is back," said a senior European NATO diplomat who was also at the alliance during the Trump years. "There was so much noise and it was a difficult time. But now we can actually talk about the things that matter, the defining security challenges of our time," the envoy said. Founded in 1949 to contain a military threat from the Soviet Union, NATO celebrated its 70th anniversary at a summit in London in December 2019. Russia, climate change, Afghanistan and new technologies are on the menu of the day-long summit, which will culminate in a special leaders" session in the amphitheatre-like North Atlantic Council chamber. "I expect Allies will agree a new cyber defence policy for NATO," Stoltenberg said. "It will recognise that cyberspace is contested at all times," he told a news conference. Having strengthened its capability to carry out its core mission of defending Europe following Russia"s 2014 annexation of Crimea, NATO now aims to be more ambitious. In a twist of fate, the NATO summit will agree reforms to the alliance, known as NATO 2030, which were set in motion after Trump questioned its relevance. Stoltenberg will set out nine areas where NATO could modernise over the medium term, including more joint allied funding of military operations. However, France has already expressed concern about the proposal, fearing it will take money away from national military priorities. read more Leaders are likely to agree to draw up a new master strategy document, known as NATO"s Strategic Concept, to include China"s military rise as a challenge for the first time.