After a year of controversy over Facebook Inc.’s role in spreading misinformation and handling violent images, Chief Executive Mark Zuckerberg now is positioning the company as the backbone of what he hopes will be a new “social infrastructure” addressing some of humanity’s biggest problems.

In a nearly 6,000-word manifesto Thursday, Mr. Zuckerberg outlined ambitions for the 13-year-old social network to play a larger role in tackling issues including terrorism, disease and climate change, alongside the work of governments, nonprofit organizations and other companies.

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Facebook is investing more in building products that can alleviate some of these issues, Mr. Zuckerberg wrote, outlining few concrete steps. He also said Facebook was developing tools to more effectively fight the spread of misinformation; detect terrorist propaganda through artificial intelligence, and to promote political engagement, both nationally and globally.

“Today’s threats are increasingly global, but the infrastructure to protect us is not,” Mr. Zuckerberg wrote. “Humanity’s current systems are insufficient to address these issues.”

The post underscores how much Facebook has evolved since its founding in 2004 in a Harvard dorm room. From its start as a social hub for college students, it has become a powerful shaper of views and an essential hub of information, social ties and communication for its nearly two billion monthly users—roughly a quarter of the world’s population.

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“For the past decade, Facebook has focused on connecting friends and families,” the 32-year-old CEO wrote in the note, published on Facebook. “With that foundation, our next focus will be developing the social infrastructure for community—for supporting us, for keeping us safe, for informing us, for civic engagement, and for inclusion of all.”

The post also comes after a trying year at Facebook, which faced criticism for, among other things, the design of its news feed, which put legitimate news sites on equal footing with those peddling misinformation during the U.S. presidential campaign.

The company also drew fire for failing to catch violent live videos and for inconsistently applying its content standards, such as when it deleted posts containing a famous Vietnam War photo of a naked girl fleeing napalm bombs last fall. After considerable public uproar, Facebook reversed that decision.