"BJP by violating its core ideology has caused break up in NDA which will harm the party the most," Nandan said in his resignation letter sent to BJP President Rajnath Singh.
Showering praise on Chief Minister Nitish Kumar for taking a backward state like Bihar on the path of development, he said BJP had joined the coalition government in Bihar by keeping away controversial issues.
"Why did BJP create a controversy by pushing forward the name of Narendra Modi?" he asked.
Amid clear indication of his joining JD(U), he lauded Nitish Kumar saying through sheer hard work he had transformed the face of the state.
Bihar is talked about with respect across the world due to the image changeover, he said and expressed faith in the leadership of Kumar.