No, it doesn't. By my reading, it obliges the signatories to respect Ukrainian sovereignty, but not defend it. Our only defense obligation is to seek UN Security Council action. But, Russia is a permanent member, so that's not going to materially change anything.

Are you sure? It says “The memorandum included security assurances against threats or use of force against the territorial integrity or political independence of Ukraine, Belarus, and Kazakhstan.” So there were assurances, not just “respect”

Here's the actual text. Note the language is mostly "so-and-so will refrain from doing something". Not "so-and-so will assist in case of something". https://en.wikisource.org/wiki/Ukraine._Memorandum_on_Securi...

The Russian Federation, the United Kingdom of Great Britain and Northern Ireland, and The United States of America reaffirm their commitment to Ukraine, in accordance with the principles of the CSCE Final Act, to respect the independence and sovereignty and the existing borders of Ukraine.

The Russian Federation, the United Kingdom of Great Britain and Northern Ireland, and The United States of America reaffirm their obligation to refrain from the threat or use of force against the territorial integrity or political independence of Ukraine, and that none of their weapons will ever be used against Ukraine except in self-defense or otherwise in accordance with the Charter of the United Nations.

The Russian Federation, the United Kingdom of Great Britain and Northern Ireland, and The United States of America reaffirm their commitment to Ukraine, in accordance with the Principles of the CSCE Final Act, to refrain from economic coercion designed to subordinate to their own interest the exercise by Ukraine of the rights inherent in its sovereignty and thus to secure advantages of any kind.

The Russian Federation, the United Kingdom of Great Britain and Northern Ireland, and The United States of America reaffirm their commitment to seek immediate United Nations Security Council action to provide assistance to Ukraine, as a non-nuclear-weapon state party to the Treaty on the Non-Proliferation of Nuclear Weapons, if Ukraine should become a victim of an act of aggression or an object of a threat of aggression in which nuclear weapons are used.

The Russian Federation, the United Kingdom of Great Britain and Northern Ireland, and The United States of America reaffirm, in the case of Ukraine, their commitment not to use nuclear weapons against any non-nuclear-weapon state party to the Treaty on the Non-Proliferation of Nuclear Weapons, except in the case of an attack on themselves, their territories or dependent territories, their armed forces, or their allies, by such a state in association or alliance with a nuclear weapon state.

Ukraine, The Russian Federation, the United Kingdom of Great Britain and Northern Ireland, and The United States of America will consult in the event a situation arises which raises a question concerning these commitments.

Edit - Russia is in breach for failing to respect Ukrainian sovereignty. The US and UK are not in breach for failing to send troops. The EU (nor any other member states) wasn't a signatory, so it doesn't apply to them at all.

No. That was merely a memorandum, not a defense treaty.

Memorandums are internationally treaties. The term has a different meaning in that context.

You’re right though, it doesn’t spell out any mutual defense statements.

Is a signed memorandum not binding then? Is it little more than hopes and aspirations?

The memorandum only required signatories to respect Ukrainian borders. It didn't contain any provisions for enforcement or defense if one of the signatories violated the memorandum. Since the US and UK didn't commit to do anything (beyond perhaps bringing the issue to the UN Security Council) then the question about whether the memorandum is binding of kind of moot.