and TV The politician who became the winner, Jair Lapid formed a union on Wednesday
Two of Israel's top rivals Benjamin Netanyahu in the April elections announced a centrist union in an attempt to defeat him.
Former Military General Benny Ganz and centrist politician Jair Lapid agreed to return as Prime Minister if they win.
Separately, Mr. Netanyahu created an alliance with several far-right parties to try to support the voices
His right-wing Likud party led the election, despite investigating allegations of corruption against him.
The Israeli general attorney must decide whether Mr Netanyahu, who denies the allegations, should be accused in the coming weeks.
Who are the contenders?
Mr Ganz, the former Israeli Defense Force (IDF) leader and TV journalist Jair Lapid, announced their intention to run for a joint center ticket on Wednesday before a deadline for submission of candidate lists for the 9 April elections.
They also joined former Defense Minister Mose Yaholon and former military chief of staff Gabi Ashkenazi.
The central settlement agreement is believed to make competition more competitive and challenging for Netanyahu's decade, BBC Correspondent in Jerusalem Tom Bateman says:
Mr Ganz's "Resilience" party said in a statement , "has decided to create a common list that will include the new Israeli ruling party," and promised to reunite Israeli society.
If he succeeds in the election, Mr Gantz has agreed to take up the post of prime minister in the first two and a half years before Mr Lapid took over.
Where is Netanyahu?
Public opinion polls suggest Netanyahu's Likud Party will win the most seats in parliament and will be able to form another ruling coalition of nationalist and religious parties.
All governments in Israel are coalitions due to the system of proportional representation of the country, which means that a party is unlikely
Who is the commander who has become a prime minister?
Israel on profile
On Wednesday, Mr Netanyahu helped negotiate the merger of the far right Jewish home and the ultra-right Jewish government. parties in an attempt to increase the total number of seats held by right-wing parties after the election.
As part of a union with his party in Likud, he agreed to cancel two cabinets for the Jewish home party, as long as he agreed to the merger.
However, his critics condemned the decision to join forces with the Jewish authorities, which includes students of the late anti-Arab racist Meir Cahane.
The Rabbi born in the United States headed right-wing fundamentalist groups in the 1
980s who defended attacks against the Arabs and later declared illegal under Israeli counter-terrorism legislation
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What are the accusations against P. Netanyahu?
Mr Netanyahu's campaign is overshadowed by the possibility for the Advocate General to accept police recommendations to accuse him of suspicion of fraud and bribery in three cases.
The prime minister pledged to remain in office, regardless of the Chief Prosecutor's decision.
If he wins, he will be about to become Israel's longest leader by taking on the title of David Ben-Gurion.