> mainly US
You missing historical order here. Ukraine gave up their arsenal long before they decided to drop Russia as an ally and play with Europe/USA (latter happens after "Maidan"). So at given time point (when Ukraine signs memorandum) they done it with _only_ Russia' protection in mind (as there was single country in past and they're both slavic)
> By 1996, Ukraine transferred all Soviet-era strategic warheads to Russia.
> Ukraine received extensive assistance to dismantle ICBMs, ICBM silos, heavy bombers, and cruise missiles from the __U.S.__ funded Cooperative Threat Reduction Program
Citing wiki: > Euromaidan was a wave of demonstrations and civil unrest in Ukraine, which began on the night of __21 November 2013__ with public protests in Maidan Nezalezhnosti (Independence Square) in Kyiv
Easy, uh?
The only convoluted thing here is your own history as you see it.
> Russia was considered the biggest threat to Ukraine independence starting with Kyivan Rus'
Until Yushchenko there was no such president. Relations never were stable, though.
Look at A.I. Kuzmuk paper "Ukraine military doctrine evolution" if curious. VDU-1993 and VDU-2004 never considered Russia as a threat. VDU-2004 states there is no direct military threat against Ukraine, just possibility of being involved into bigger conflict. Kuchma even cancelled statement about NATO integration in VDU-2004, by making it more smooth.