Back in 2007, Microsoft famously attempted to acquire Yahoo!, but settled for the Bing-Yahoo Search Alliance, which placed Bing Search and ads on the Yahoo Network. The 10 year deal remained contentious through most of its run, with at the time Yahoo leader Marissa Meyer trying to get out of the agreement, and restructuring it halfway through.
Fast forward to today, and the news that with Microsoft's recent partnership with Verizon, who now owns Yahoo, Bing Ads will be the sole ad provider for all of Verizon's properties:
Microsoft and Verizon Media are making it even easier for search marketers to reach valuable audiences across the Bing Network through an expanded partnership. As a result, marketers will have a single global platform to create search advertising campaigns that reach audiences across the Bing, Yahoo, and AOL networks. All search advertising opportunities across Verizon Media properties, including campaigns on both Yahoo and AOL, will be exclusively served by Bing Ads.
Microsoft is expecting the partnership to result in "an increase in clicks across the Bing Ads marketplace for customers targeting the United States of up to 10-15%," with a full transition of worldwide traffic to be complete by March of this year.