Facebook Inc.’s somewhat controversial move to shift its messaging capabilities into a separate app seems to have panned out. Facebook Messenger has reached over 500 million users this week, which is more than the population of the US and Canada combined.

It is also only 100 million users fewer than popular messaging app WhatsApp, which Facebook bought for $19 billion earlier this year.

Facebook’s messaging app has been in the news a lot lately, but it has actually been around for a few years. It originally launched on iOS and Android just over three years ago, but it was relatively unimportant until a few months ago when Facebook decided to remove messaging capabilities from its main app, forcing users to adopt Facebook Messenger if they wanted to continue chatting with their friends and family through the social network.

At the first ever Facebook community Q&A held last week, the first question asked of Facebook CEO and co-founder Mark Zuckerberg was: “Why did you force us to use Facebook Messenger?”

Zuckerberg explained that he understood the move was a “big ask,” but he felt the change was necessary.

More people used Facebook for messaging than for anything else, but he was dissatisfied with the way messaging previously worked in the core Facebook app.

He said that the old process of getting an alert, opening the Facebook app, changing to the messaging tab, and opening the message was too cumbersome and inefficient. A dedicated messaging app, he explained, would speed up the process and put messaging through Facebook at the same level as SMS messaging.

Even though 500 million seems like an enormous number, it represents roughly half of Facebook’s total user base.

At the Q&A last week Chris Cox, Facebook’s head of product development, discussed the effects of new products and updates on such a large amount of users.

Cox said:

In the billion people that are using Facebook, you can oftentimes build something that 100 million people will love. […] That’s a really hard number to think about.

Since the removal of messaging from the Facebook core app, the rating for Facebook Messenger on iOS dropped to just 1.5 stars.