The worlds richest 500 people increased their collective wealth by 25% in 2019 a stark reminder of worsening income inequality, particularly in the U.S.

The 500 wealthiest people held a net worth of $5.9 trillion dollars collectively up $1.2 trillion over this year alone, according to the Bloomberg Billionaires Index . Topping the list of richest people were familiar names: Amazon founder Jeff Bezos, followed by Microsoft founder Bill Gates, French luxury group head Bernard Arnault, Berkshire Hathaway CEO Warren Buffett and Facebook co-founder and CEO Mark Zuckerberg.

This news comes as income inequality and wealth concentrating in the hands of the few has become a much-discussed topic in the 2020 Democratic presidential race.

There are two billionaires among the Democratic 2020 contenders: California hedge fund manager Tom Steyer and former New York City mayor and businessman Michael Bloomberg (whose news site publishes this daily ranking of the worlds wealthy ).

Bloomberg News said it would stay out of investigations in the 2020 race after its founder and owner became a contender earlier this year but broke its own rule earlier this week in a report on progressive rivals Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.).

Sanders and Warren are among the candidates who most often criticize the economic and political systems that allow the nations income gains to disproportionately accrue to the wealthy.

One of Warrens flagship policy proposals would target the ultra-wealthy with a 2% tax on fortunes larger than $50 million. Sanders, in a conversation with the Los Angeles Times editorial board published this week, called out how despite there being a low unemployment rate in the U.S., wages have largely stagnated for decades , leaving many Americans struggling to get by.

A study earlier this year found that the 400 richest people in the U.S. owned more than the 150 million people in the bottom 60% of the country and that since the early 1980s, those 400 richest Americans had tripled their wealth.