Comparisons with Poland, 1939, are not really useful. The poles made many errors in planning and were certainly outclassed in regards to much equipment but the country was surrounded on 3 sides by enemies, 2 of which invaded the country 17 days apart (the invasion by the red army was no peaceful intervention), and Poland believed it had a treaty guarantee underpinning its sovereignty. Moreover, the 1939 blitzkrieg legend is more myth than fact. Regardless, the Germanicon and Soviet victory was decisive but poland held out for 5 brutal weeks, losing some 80,000 military dead and 100,000+ civilians killed. One of the best, most comprehensive english language treatments of the Polish campaign is Roger Moorhouse's Poland 1939. It is an excellent start to the correction necessary.
Crimea, on the other hand, was a completely different context, as was the original war in eastern Ukraine. Most importantly for this discussion, there was no unified front supporting a hard line with Russiaicon. In addition, Ukraine has spent 8 years studying and fixing many of the problems that hindered an effective response to the start of the war with Russia (in 2014--they don't see a break in hostilities). 'The west' helped in that period but we should not overstate our diplomatic, economic, or military assistance. The measures Ukraine has taken are not well described in the English language material. Deterrence is a tricky business, to put it lightly, and any use of historical analogies is more likely to result in miscalculation than success.