An expected venture between General Motors of the United States and French group PSA Peugeot Citroen is set against the background of severe restructuring by many groups in response to the recent global financial crisis.

In the last 25 years, takeovers, deals and alliances have periodically changed the landscape of the global auto industry as manufacturers adapted to competition, first from Japan and South Korea, then seized opportunities in eastern Europe and also focused on emerging markets.

Here is a list of the world's biggest car groups based on units sold in 2011.

1. General Motors regained the top spot in 2011, selling 9.03 million vehicles. Chevrolet, Opel-Vauxhall, Buick, Cadillac and GMC are its main brands.

GM has a global staff of 202,000 people and reached sales of $150.3 billion (111.33 billion euros) in 2011.

2. Germany's Volkswagen is Europe's biggest car group and has stated its ambition to unseat GM as the world's number one by 2018.

In 2011, it sold more than 8.0 million vehicles for the first time, selling 8.3 million.

Top brands are Volkswagen, Audi, Seat, Skoda, Bugatti, Lamborghini and a large stake in Porsche.

The group employs 400,000 people and reached sales of 159.3 billion euros last year.

3. Franco-Japanese alliance Renault-Nissan sold 8.03 million vehicles in 2011, if sales at Russia's Avtovaz, 25-percent owned by Renault, are included.

Renault alone employs 128,300 people worldwide and posted sales of 42.63 billion euros in 2011.

Nissan, 43.8-percent owned by Renault, has 155,000 employees and has forecast sales of 9.450 trillion yen (87 billion euros, $117.4 billion) for its current fiscal year which ends March 31.

4. Hurt by the earthquake and tsunami disaster, Japan's Toyota sold 7.95 million vehicles in 2011, losing its position as the world's biggest carmaker which it held from 2008 to 2010.

Toyota, which also makes the Lexus, employs 317,700 employees worldwide and estimates sales of 18.3 trillion yen at the end of the fiscal year in March.

5. South Korea's Hyundai and Kia, its 39-percent owned partner, sold 6.6 million vehicles last year.

Hyundai posted sales in 2011 of $69 billion and Kia $39 billion.

6. The second largest carmaker in the US, Ford sold 5.7 million vehicles last year. It employs 164,000 people and posted sales of $136.3 billion in 2011.

7. The new alliance of Italy's Fiat and the US-based Chrysler together sold slightly fewer than 4.0 million vehicles in 2011. The alliance aims for sales of 6 million units in 2014.

Fiat posted sales in 2011 of 59.56 billion euros, which included seven months of sales by Chrysler. Fiat employs 190,000 and Chrysler more than 52,000.

7. France's PSA Peugeot Citroen sold 3.5 million vehicles in 2011. It posted sales of 59.9 billion euros last year and employs 205,000 people.

8. Japan's Honda sold 3.095 million vehicles last year. It employs 179,000 people and forecasts sales of 7.850 trillion yen by the end of the fiscal year on March 31.