"Never in modern history have we gone so many years without a military confrontation between the major powers", UN Secretary-General Antonio Guterres told the summit meeting commemorating the world body's 75th anniversary.

That has undoubtedly been the greatest success of the United Nations, although it has also made big contributions to human rights through the promotion of decolonization, disease eradication, poverty alleviation and environmental protection.

That all 193 members reiterated in one voice the central role of the UN and collective commitment to multilateralism was an impressive feat at a time of stark divisions.

But as the declaration they released stated, "multilateralism is not an option but a necessity ..."

As the UN chief lamented, "We have a surplus of multilateral challenges and a deficit of multilateral solutions."

With the world's frailties laid bare by the novel coronavirus, the real test going forward is whether the signatories to the declaration can achieve the "reinvigorated multilateralism" they envisioned.

The fact that the United States president did not even bother to speak at such an important occasion on such a significant subject vividly illustrates the extent of the divisions. Instead, the acting deputy UN ambassador used the occasion to air the US administration's now familiar complaints.

The tensions between veto-wielding permanent members of the UN Security Council, in particular, greatly constrain the world body's functioning.

President Xi Jinping called on the UN to focus on problem solving and tangible outcomes, and big countries to "lead by example". He again stated the need to "replace conflict with dialogue, coercion with consultation and zero-sum with win-win".

Yet those very constructive proposals are very difficult to implement considering today's global context.

The sad truth is a certain major country is setting a very bad example, even threatening the global governance regime. Rules and institutions governing international relations are being brushed aside. Exceptionalism and double standards run riot. Unilateralism takes the place of multilateralism.

German Chancellor Angela Merkel was correct in saying "the United Nations can be only as effective as its members are united". Disunity between major members, particularly at the Security Council level, is the biggest stumbling block on the UN's way toward continued relevance.

None of the world's burning imperatives, from the pandemic to security risks to climate change, can be properly addressed with key stakeholders remaining as divided as they are.

"We face our own 1945 moment," the UN chief said. "We must meet that moment. We must show unity like never before to overcome today's emergency, get the world moving and working and prospering again."

Which as the Chinese president stressed means, "there must be a cure, not just therapy"; countries "must act, not just talk".