Some 123 countries are part of the 2008 International Convention on Cluster Munitions which bans the use or transfer of this particular weapon.

Almost all of America's allies are signatories to the convention.

Even within US government circles, there has been deep unease about supplying its own stockpile of cluster munitions to Ukraine.

Ukraine war latest: US to send Kyiv controversial weapon banned by more than 100 countries

As recently as last week, within the state department, there was division about the decision to supply the weapon.

The long and grim record of the cluster bomb explains the unease and the controversy.

Globally, civilians represent 97% of cluster munition casualties, according to a report last year by the Landmine and Cluster Munition Monitor - an organisation that seeks to ban them altogether.

Children are overwhelming the victims.

By supplying the weapon, there is a clear risk to civilians, not now necessarily, but in the future. The legacy of unexploded cluster bomblets is evident on former battlefields globally.

America also risks losing the moral high ground against Russia by supplying a weapon banned by much of the world.

So why supply it?

Well, the facts on the ground are not in Ukraine's favour. The transfer is a clear signal that the war is not going well for Ukraine.

The so-called spring offensive did not materialise in the spring and looks set to falter through the summer too.

Ukraine is fast running out of more conventional artillery with supply stocks in America and elsewhere running low.

A 'bridge of supply' is necessary.

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America holds a vast dormant stockpile of cluster munitions. They could shift the momentum significantly on the ground, wiping out heavily dug in Russian troops.

American officials are accepting that a legacy of civilian casualties is a risk but counter it by arguing that more civilians are at risk by allowing Russia to occupy Ukrainian land.

The munitions would be used by Ukraine on occupied Ukrainian soil. The risk to civilians would be owned by Ukraine. The onus would be on Ukraine, with a pledge of American help, to clear the unexploded munitions when the war comes to an end.

The announcement is part of a multi-million dollar tranche of new weaponry which is an attempt by the Biden administration to future-proof the conflict; to give Ukraine the weapons it needs now in case domestic political circumstances change in the next 18 months.

American politics is in flux.

There is no guarantee of open-ended support for Ukraine.