Why don't signatories of Budapest Memorandum on Security Assurances (except Russia) protect Ukraine with force?

Question

The Budapest Memorandum on Security Assurances is a political agreement providing security assurances by its signatories relating to Ukraine's accession to the Treaty on the Non-Proliferation of Nuclear Weapons. The Memorandum was originally signed by three nuclear powers, the Russian Federation, the United States of America, and the United Kingdom. China and France gave somewhat weaker individual assurances in separate documents.

The memorandum included security assurances against threats or use of force against the territorial integrity or political independence of Ukraine.

Why don't signatories protect Ukraine from Crimea and Eastern Ukraine Russian invasion?

Answer 1

The most accurate answer would be: they do, despite they are not obliged to.

The text of Budapest Memorandum says:

4. 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;

Many analysts say that neither U.S. nor U.K. officials believed that their lawmakers would ratify an obligating international treaty, so they mutually agreed to make the Budapest Memorandum a political agreement.

Quoting Steven Pifer's interview to CNN:

„…neither the George H. W. Bush administration nor the Clinton administration was prepared to extend a military commitment to Ukraine — and both felt that, even if they wanted to, the Senate would not produce the needed two-thirds vote for consent to ratification of such a treaty.
The Budapest Memorandum thus was negotiated as a political agreement. It refers to assurances, not defined, but less than a military guarantee. U.S. negotiators — myself among them — discussed this point in detail with Ukrainian counterparts so that there would be no misunderstanding.“

At the time, this form of agreement seemed adequate for the political situation. However, after Russia invaded Ukraine and occupied the Crimean peninsula, it became clear that a weak reaction to Russian aggression would ruin the whole system of international agreements of such kind.

As I mentioned in another answer, there are many countries who have or had their nuclear programs: consider Iran, Libya, Pakistan, Egypt, Argentina, Brazil, and South Korea.
They all have territorial disputes with their neighbors, and in some cases these neighbors are already nuclear countries (see, for instance, India versus China).
Obviously, the nuclear states put huge efforts to non-proliferation programs in these countries. The only way how this can be accomplished is by providing these countries with some guarantees, similar to those stated in Budapest Memorandum.
If the signatories of Budapest Memorandum did not help Ukraine, this would be clear indication that
the only way to protect your interests is The Bomb.

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Having that said, the signatories of the Budapest Memorandum do help Ukraine in unprecedented amounts:

• Sanctions: The U.S. has introduced massive sanctions against Russia's economy, which led to losses of $0.2 trillion (official information by Russian propaganda) to $0.75 trillion (analysts) only during Q2-Q3-Q4 2014.
  It should be mentioned that American and European economies also suffer from cancelled contracts and missed opportunities, so this step is not as easy as it seems to be.
• No More Collaboration: France has cancelled a €1.2 billion arms sale: two "Mistral" helicopter carriers.
• Political Support: Russia has been expelled from G7 and G20 — a huge political defeat.
• Military Support: U.S., Canada, and European countries (on individual basis or within NATO) are providing Ukraine with non-lethal military support.
• Arms: U.S. Senate Armed Services Committee and The House passes defense policy bill that includes $300 million in military assistance to Ukraine, including lethal weapons.

The United States, as Ukraine continues to defend itself against the Russian aggressor, is committed to being a steadfast partner. We have provided $266 million dollars in security and defense-related assistance since Russia’s invasion of Crimea in 2014.
This year [2016], we expect to provide an additional $335 million in training and equipment to our Ukrainian partners. This new assistance, provided by the U.S. Congress, will allow us to expand U.S. training at Yavoriv and Khmelnytskyi, and to deliver needed military equipment to improve Ukraine’s defensive capabilities on the front lines.
— Geoffrey Pyatt, U.S. Ambassador to Ukraine

• Intelligence: U.S. shares their intelligence data, including satellite reconnaissance, with Ukraine's General Staff (an unprecedented action).
• Peacekeeping Mission: UN is currently discussing sending UN peacekeeping mission to occupied territories of Ukraine.
• U.S. and NATO instructors are coming to teach Ukrainian army.
• Financial Aid: IMF and G7 are preparing a new $40 billion package of economic aid to Ukraine. updated on 2015-03-11: the initial $17bn have been approved.
• Moody's and S&P have already downgraded Russia's credit rating below junk level. By itself, this means no future investments, plus the vast majority of existing investors would demand preliminary closure of investment programs because most credit agreements have covenants linked to ratings assigned by one or more rating agencies.
• Other Aid: U.S. has started many programs to help Ukraine, including:
  • Humanitarian assistance.
  • Security sector improvement.
  • Economic stabilization.
  • Energy security.

See this fact sheet for more actions in place. (note, it is a bit backdated, September 2014)*

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Summary

Although many see the Russian invasion as just a small Russian-Ukrainian war, it is not.
In fact, Russia has effectively declared war on the rest of the world. This video (Youtube) has been broadcasted on Russian propaganda TV channel on February 8, 2015 during prime time (English subtitles).

Instead of the direct ignition of a military standoff on Ukrainian soil, the signatories of Budapest Memorandum have chosen a more effective way of eliminating the Russian treat. This includes several aspects:

• Political — Russia's expulsion from international organizations, reducing their role in the United Nations Security Council.
• Economical — sanctions, oil prices, etc.
• Legal — currently open investigations of acts of war and terrorist activity.
• Humanitarian — helping Ukraine to avoid a crisis caused by foreign invasion.

This looks quite similar to how the world has eliminated the previous Russian project, a militarist "USSR", and the outcome is supposed be similar as well.

Answer 2

They don't do it because it's quite plainly not what it was intended for. An alliance or treaty with strong guarantees is worded completely differently. As an example, here is the beginning article 5 of the NATO treaty:

The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.

It also includes many dispositions to spell out the details of the alliance, what counts as an aggression, etc.

By contrast, here is the most relevant part of the Budapest Memorandum:

The United States of America, the Russian Federation, and the United Kingdom of Great Britain and Northern Ireland, 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.

It's basically a commitment to do… nothing or almost nothing. If you take it literally, the only thing that should happen is that the three countries in question should “consult” over this matter and possibly co-sponsor a resolution in front of the UN security council. But Russia has a veto there and certainly does not agree that any aggression has taken place. And note that the memorandum only refers to “an aggression […] in which nuclear weapons are used”, which isn't the case, even if we ignore Russia's denials of its involvement.

And a good reason why the memorandum does not provide stronger guarantees is that it seems like an awful idea. It's probably a bit simplistic but strong alliances have been blamed for the scope of the First World War. You can't expect anybody to commit to go to war or risk an all-out military confrontation over Ukraine. Vague promises made twenty years ago aside, it still does not sound like a good idea today.

Frankly, the most surprising thing is how much weight people seem to give to this memorandum.

Answer 3

Because you risk turning a small war between Russia & Russian backed separatists in to something much bigger (at worst a full nuclear exchange) and at best you've gained nothing important and lost a few thousand soldiers, some expensive equipment, a lot of money and have just propped up a country full of Nazi supporters.

Any politician that did that would commit political suicide the second your soldiers started coming back in body bags.

And why stop at Russia? Why not free Tibet, eliminate ISIS, eliminate boko haram, invade North Korea, invade Saudi Arabia (who do you think is funding Muslim extremists all over the world?), invade Israel, defend Iraq against the USA's illegal invasion in the second gulf war, invade Pakistan for harboring Osama bin Laden and dozens more countries that are doing things that you don't like.

Answer 4

If for no other reason than because the Ukraine is too far away from other US military-controlled assets. Said another way: there's a limit to US power, and the Ukraine is beyond that limit.

Answer 5

Why don't signatories protect Ukraine from Crimea and Eastern Ukraine Russian invasion?

Because that agreement is a con: not a single of its signatories intended to fulfill its obligations under that agreement. Its sole purpose was to get the Ukrainians to surrender their nuclear weapons.

too bad that the Ukrainians fell for it. a great outcome for everybody else.