Billionaire Bill Gates has spent the past two decades warning the public about grim issues, from looming "climate disasters" to "catastrophic cyberattacks."

Two potential disasters, however, worry Gates the most. "Many disruptions" in today’s world could trigger "a major war," Gates told CNBC Make It. "Even if we avoid a big war, there will be another pandemic, likely within the next 25 years."

Scientists generally categorize pandemics as "likely" or even "inevitable" events over time. As the years go by, they become increasingly frequent due to climate change and rising global populations, according to research.

For Gates, the question isn't whether another pandemic will happen soon, but whether nations will be better prepared than they were for the outbreak of Covid-19. "The country the world expected to lead and set an example did not meet those expectations," Gates said, referring to the United States.

In 2022, Gates wrote a book titled How to Prevent the Next Pandemic, in which he criticized several governments, including the U.S., for being unprepared in 2020. He offered various recommendations for countries worldwide, such as implementing stronger quarantine policies, investing in disease surveillance, and boosting vaccine research and development.

While some progress has been made, including increased spending on pandemic preparedness in the U.S. and elsewhere, Gates says global governments "are still not ready." "We learned some lessons from the coronavirus pandemic, but far fewer than I had hoped, unfortunately," he added.

Political disputes, which many believe hampered the swift response to Covid-19, continue to obstruct proper preparation for the next outbreak. "We haven’t yet seriously reflected on what we did well and what we didn’t. Perhaps within the next five years, this will improve. But so far, I’ve been disappointed," Gates noted.

The prevention of widespread disease is a key focus of an episode in the upcoming Netflix documentary series, What’s Next? The Future with Bill Gates, premiering today, September 18.

In the Netflix series, Gates speaks with Dr. Anthony Fauci, former Director of the National Institute of Allergy and Infectious Diseases. In their discussion, Fauci argues that wealthier nations, like the U.S., have a "moral responsibility" to share their abundant resources and lead efforts to prevent the global spread of diseases.