Contradiction with Proverbs 6:16-19
While Nehemiah 6:18 speaks of alliances through marriage, these verses list behaviors that the Lord hates, including sowing discord among brethren, which can result from such alliances.
Proverbs 6:16-19: These six [things] doth the LORD hate: yea, seven [are] an abomination unto him: [unto...: Heb. of his soul]
Contradiction with 2 Corinthians 6:14
Nehemiah 6:18 notes alliances with non-Israelites, while this verse advises against being unequally yoked with unbelievers.
2 Corinthians 6:14: Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?
Contradiction with Exodus 34:12-16
Contradicts Nehemiah 6:18 by warning against making covenants with inhabitants of the land, as they may lead Israelites to sin through intermarriage.
Exodus 34:12-16: Take heed to thyself, lest thou make a covenant with the inhabitants of the land whither thou goest, lest it be for a snare in the midst of thee:
Contradiction with Deuteronomy 7:3-4
Commands Israelites to not marry with foreign nations to avoid turning away from God, contrasting with the alliances formed in Nehemiah 6:18.
Deuteronomy 7:3-4: Neither shalt thou make marriages with them; thy daughter thou shalt not give unto his son, nor his daughter shalt thou take unto thy son.
Contradiction with Ezra 9:1-2
Highlights the issue of intermarriage with foreign lands as a sin, directly opposing the practice mentioned in Nehemiah 6:18.
Ezra 9:1-2: Now when these things were done, the princes came to me, saying, The people of Israel, and the priests, and the Levites, have not separated themselves from the people of the lands, [doing] according to their abominations, [even] of the Canaanites, the Hittites, the Perizzites, the Jebusites, the Ammonites, the Moabites, the Egyptians, and the Amorites.