@Kust after Ottoman Empire lost these territories, there was plenty of space for settlers, so Habsburgs started settling their population in the south. In 1790s and early 1800s Slovaks started settling in southern Bačka, for various economic and social reasons and spread from there to Banat (Serbian part) and Srem. I don’t know for Romania, I don’t think I ever met a Slovak from there. I met few young Slovaks from Hungary (16-18). They all have Hungarian accent for one, names are heavily Magyarized (Surnames were in Hungarian forms and none of them had Slavic first name), I don’t think any of them spoke Slovak as their mother tongue, but still, they’re trying to preserve their heritage.