Together, the four companies would be by far the largest carmaker in the world, with sales of 15 million vehicles a year and a major presence in virtually every corner of the planet. But such a monstrous corporation would be complex and even more difficult to manage than the Renault Nissan Alliance has been.

[The Renault Nissan Alliance is threatened by both companies’ fierce pride and rivalry]

The relationship between the French and Japanese has been tense since the arrest of Carlos Ghosn, the head of the alliance, in November on accusations of financial wrongdoing and his eventual ouster. Mr. Ghosn has said he is innocent.

The French have pushed to join Renault and Nissan more closely by putting them under the same holding company, but the Japanese brusquely refused that proposal. Nissan, which makes more cars than Renault, has expressed discontent with French dominance of the partnership and sought more autonomy.

The merger could also create tensions with Nissan in the United States, where the Japanese compete fiercely with Fiat Chrysler in the all-important market for SUVs and pickups. Last year Fiat Chrysler was in fourth place in the United States with 12.6 percent of the market, while Nissan had 8.4 percent.

With Fiat Chrysler on board, the alliance would be tilted more toward Europe. At the same time, the French government would have less sway over the new company than it does over Renault. French government influence has been a sore point for Nissan.

In Europe, the new company would effectively be in a tie with PSA Group, the maker of Peugeot, Citroën and Opel cars, for second place behind Volkswagen. That would put additional pressure on Ford of Europe, which has lost market share and reported a pretax profit margin of less than 1 percent in the first three months of 2019. Ford’s share of the European Union car market is 6.3 percent, compared with 16.8 percent for Fiat and Renault combined.

Under Fiat’s proposal, shareholders of Fiat Chrysler would share a dividend of 2.5 billion euros, or $2.8 billion, that reflects the company’s higher value on the stock market.

The company would be based in the Netherlands, known for its favorable corporate taxation rules. Shares of the new company would be listed on exchanges in Paris, Milan and New York.