Yadav organised the convention, titled 'Sanjhi Virasat Bachao' (save the common culture), amidst his strong opposition to Kumar joining the BJP-led NDA and his claim to represent the real JD(U).
The convention was attended by Congress vice president Rahul Gandhi and leaders from other parties like CPI-M, CPI, SP, BSP, NCP, RJD, NC, JD-S and RLD.
Yadav, who has been removed by Kumar as leader of the party in Rajya Sabha, has been insisting that he is founder of the party and hence the real leader.
As the other opposition leaders called for a united fight, Yadav urged the youth and farmers in particular to make right use of their "power of vote" for a bright future.
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"I am confident that when people of this country, world stand united, even Hitler cannot win," he said amid cheers from his supporters.
At the convention, he was lauded by many opposition leaders for standing with the secular forces and some of them recognised Yadav's faction as the "real JD(U)".
He appealed to the youth to join the "battle" for saving the composite culture.
"I want the youth to come to join the battle to save the composite culture. They (BJP) talk about 'love jihad'. What will transpire between a young boy or girl, if not love?
"I had seen the film Mughal-e-Azam years ago. It had a song 'Mohabbat Zindabad' (hail love). Now, here is a strange King who says you will go to jail if you fall in love," he said, without naming anyone or a party.
"Don't target the dalit youngsters who are fighting against the injustice...The composite culture talks about embracing the deprived," he added.
He further wondered how the country will fight against China "which is using aggressive language these days" if it is divided on communal lines.
"We cannot give a reply to China, if 80 per cent of the (country's population) youngsters, the deprived sections, farmers are not strong," he added.