If Ukraine invites NATO or the US to help defend itself against Russia, that's their right and certainly appropriate.
Would you take the same position if Russia or China signed treaties with Mexico and the provinces of a divided Canada and based its troops along our borders?
Do we threaten Mexico or Canada with annexation? Of course not. Ask that question when we do threaten Mexico and Canada.
Certainly that's their right, but does it make sense for NATO or the US to go to war on Russia's doorstep on behalf of Ukraine -- a significant portion of which favors an alliance with Russia? That's what is at issue here.
Do we threaten Mexico or Canada with annexation? Of course not. Ask that question when we do threaten Mexico and Canada.
Do the battles of Monterrey, Tabasco, Veracruz and Chapultepec or the American military occupation of Mexico City ring any bells? We invaded Mexico in the 1840s and then "annexed" most of what is now the Western US. And just prior to WWI, President Wilson ordered the US Army into Mexico during the "Punitive Expedition" of 1916-17 -- which was actually our intervention into the Mexican Civil War.
During the War of 1812, we invaded parts of Canada since they were British soil and launching points for British attacks on American territory and shipping. And on many occasions throughout the 19th and 20th Centuries, we have intervened militarily in numerous Central and South American countries when it served our interests.
So Russia must do what we say, and not what we do?