Ezra 9:1 & 2
After these things had been done, the leaders came to me and said, 'The people of Israel, including the priests and the Levites, have not kept themselves separate from the neighboring peoples with their detestable practices, like those of the Canaanites, Hittites, Perizzites, Jebusites, Ammonites, Moabites, Egyptians and Amorites. They have taken some of their daughters as wives for themselves and their sons, and have mingled the holy race with the peoples around them. And the leaders and officials have led the way in this unfaithfulness.'
At the end of chapter eight, we saw all of Israel offering sacrifices in worship of God. Now, we see that they had been living in disobedience to God's instructions regarding marriage. In Deuteronomy 7:4, God had instructed them to drive out the people living in Canaan and to remain separate from them. They were even told that it was for their own good as the Canaanite women would lead the men to worship other gods (commit idolatry). Solomon married one of these women and the result was the division of the kingdom. Now, all of the people (even the priests and servants of God) had disregarded the instructions of God. The same type of thing is happening even more today as we even have people marrying others of the same sex even though God says it is wrong. It is sanctioned by governments and even religious leaders are joining in but it directly contradicts the words of God. Israel did not take His words seriously and so were judged for it. Do we think that we are any different as a nation or world?