Yitzchak granted Yaakob the blessing that all nations would come to serve the people who would emerge from his descendants. However, Yitzchak indicated that this blessing would come true only if the Bnei Yisrael adhered to the Torah of Hashem. Once the Jews abandoned the ways of the Torah their enemies would gain superiority over them.
History has borne out this prediction. While the Jews acted properly, they enjoyed the graces of Hashem and were granted the presence of His Beit Hamikdash. However, when they refused to heed His warnings to repent, they suffered the loss of the Holy Temple and were reduced to living under gentile oppression in exile. Later, Jews tried to assimilate and become like the citizens of foreign countries such as Greece, Rome., Russia, and Germany. What they forgot was that the gentiles, the sons of Esav, have always been their enemies. As a result, all attempts of the Jews to assimilate have been met by oppression, pogroms, and wars. It was only when Jews remembered that they are Jews and tried to comply with the laws of the Torah, that they emerged supreme. self confident, and happy.