This question smells slightly of cherry-picking. First of all, Nikola Tesla was born in Croatia when it was still part of the Austro-Hungarian Empire (in fact he went to university in what is now Graz in Austria), and also both Nikola Tesla and Marie Curie made their groundbreaking discoveries once they had already left their home countries.

Also, the number of physicists from Eastern Europe, even if we only look at the era Tesla and Curie lived in, ie the early 1900s, pales into comparison with the number of scientists from countries such as Germany. Of the great scientists of the age, you have Max Planck, Werner Heisenberg and Albert Einstein (Germany), Niels Bohr (Denmark), Hendrik Lorentz (Netherlands), Louis de Broglie (Belgium), Ernest Rutherford (New Zealand), Paul Dirac (UK) etc etc.