Depends on how small the Eastern European countries you’re referring to are.

I personally believe that any country with a population under 80 million people is essentially irrelevant in global politics barring specific circumstances, and should probably merge with its neighbors to get more leverage for development.

I’ve written earlier that:

Countries <80 million have markets that are too miniscule to be good bargaining chips when negotiating with capitalist companies, unfortunately eliminating the option of pressuring foreign companies into technology transfer agreements ala China. This hurts their industrial and technological growth, placing them at the mercy of larger countries’ tech.

Countries that small also do not have enough workforce and internal market to foster vibrant, holistic domestic industry on their own. There simply is not enough money or workforce to cultivate the funds necessary to conduct advanced R&D to continuously keep up with the world in all aspects of industry. Oftentimes, this forces small countries to import most of their manufactured goods.

Lastly, countries that small also do not have enough money or workforce to build up militaries strong enough to go toe to toe against 100+ million population countries. While they may be strong enough to defend the country itself, they are not able to be expeditionary and act on geopolitical objectives abroad. If under threat, small countries ultimately have to seek protection from allied larger countries, again jeopardising sovereignty.

For these reasons, it is imperative for small countries to form unions to get to ~100 million population. At that size, they have the weight to push for industrial development and geopolitical interests.

Some countries are already doing this. Mali, Niger, and Burkina Faso have formed the Alliance of Sahel States, with a total population of 71 million, for the express purpose of establishing a common market, industrialization, military cooperation, and eventually unifying into a single sovereign state.

Of course, merging into larger states is unlikely to happen under bourgeois control because national bourgeoisies like to enjoy the minor insignificant spoil of leading a tiny country rather than joining up for the greater good. Also, Western capitalist powers enjoy the ease of pushing around these tiny countries, which might become harder to push around if they merged into larger collectives.