When Google debuted on Wall Street on Aug. 19, 2004, the public market was still scratching its head at what the company could do, let alone what a search engine was.

Fast forward 15 years — and more than 200 acquisitions later — Google has become a verb and part of many people's daily lives. But some politicians and regulators are now trying to stem that power by forcing it to unwind some of those acquisitions.

Last month, the Department of Justice announced a broad antitrust review of big-cap technology companies. In the months prior, Democratic presidential hopeful Sen. Elizabeth Warren proposed a plan that included divesting Google's acquisitions of Nest, Waze and DoubleClick. In fact, Warren mentions the term "Google" 16 times in her proposal.

"Google has snapped up the mapping company Waze and the ad company DoubleClick," Warren wrote. "Unwinding these mergers will promote healthy competition in the market — which will put pressure on big tech companies to be more responsive to user concerns, including about privacy."

Here's a rundown of the biggest and most successful buys Google has made since its IPO.

DoubleClick: The most obvious target for antitrust concerns is DoubleClick, which Google bought in 2007 for $3.1 billion. It provides a lot of the technology behind its core advertising business, which constitutes 80% to 90% of Alphabet's total revenue — nearly $100 billion a year.

Waze: Google bought Israeli start-up Waze in 2013 for $1.1 billion, which has brought social traffic data that has helped Google Maps predict travel times and routes. Today, it has over 100 million monthly active users. Some argue that by owning both Waze and Google Maps, the company has too much control over mapping data

Nest: Google bought smart home company Nest for $3.2 billion in 2014. Since then, it has turned what was a smart thermostat product into Google's home devices brand, which includes smart thermostats, smart lights and smart speakers. Earlier this year, watchdogs notified the Federal Trade Commission of data privacy concerns.

YouTube: Google paid $1.65 billion for the video-sharing site in 2006. At the time, it had fewer than 100 employees. While it's grown to become Google's second-largest revenue contributor, with estimated revenues of $15 billion a year, it still has too few employees to deal major issues it faces, according to lawmakers. Both sides of the aisle have increasingly vocalized their concern that the video platform has grown too big to properly control the spread of violent content and misinformation.

Android. Another successful buy was Android, which Google picked up in 2005 for $50 million. Open-sourcing Android helped allowed Google's operating system to live on a variety of mobile devices from mobile carriers around the world, accounting for 85% of the smartphone market share, according to research firm IDC. Along the way, many Android resellers also picked up related Google mobile services like search and Gmail — and the mobile advertising revenue that goes with them.

As for acquisitions that didn't work out so well, analysts have pointed to Slide, a social app developer that Google shut down two years after buying it for $182 million.

The grayer areas include Motorola, which at first seemed like a bust — Google paid $12.5 billion in 2011 and sold it for $3 billion two years later. But, it did give Google some useful patents to compete against Apple in the smartphone wars.

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