For example, Russia's recent behavior suggests that it doesn't have a similar view to the US on warfare and competition, said Jerry Hendrix, director of the Center for New American Security Defense Strategies and Assessments program.
Russia's maneuvers into Crimea and Ukraine were hybrid warfare, with "little green men" and some standoff intelligence, surveillance and reconnaissance (ISR) capabilities, he said. In Syria, Russia has been not been using precision strike weapons or laser-guided bombs, but dropping "dumb bombs."
"What we saw with Russia moving into Syria I think tells us that these things can turn left or right, but not follow along the same track that we would expect them," Hendrix said.
Hendrix's remarks came Monday at Setting the Next Defense Agenda, the inaugural national security forum hosted by CNAS.
In the Baltic, Russia's advances in Anti-Access/Area Denial (A2AD) have run counter to the US' strategic bet that it would be operating in permissive environments, he said.
"We are behind in adapting to that," Hendrix said of Russia's A2AD efforts. "We have lagged strategically in our approach."
Elbridge Colby, a senior fellow at CNAS, emphasized Russia and China's evolving approach to nuclear weapons. For example, Russia has been contemplating the limited use of a nuclear weapon to end a conflict, he said. Chinese plans possibly involve developing superior strength in the Pacific through conventional weapons, requiring the US to escalate to nuclear weapons if it wants to reclaim military superiority, he said.
"Any conflict that involves the United States and China or the United States and Russia is going to involve nuclear weapons," he said. "This means having a defense strategy that very clearly and practically has ways of plausibly deterring an adversary from using nuclear weapons, or god forbid if they have been used, terminating their usage in terms that are favorable to us."
Michael C. Horowitz, a political science professor at the University of Pennsylvania, pointed to the proliferation of unmanned or autonomous systems as one of the most important trends in national security.
"This technology is spreading, and it is spreading quickly," he said.
Particularly with the use of autonomous systems, the dynamics of the battlespace are speeding up because decision cycles are getting shorter, he said. Often, when a crisis emerges, it doesn't often escalate to war because cooler heads have time to prevail, he said.
With autonomous systems in play, either there isn't time for cooler heads to de-escalate a situation, or people have been removed from the decision-making loop already, he said.
The US must develop strategies that incorporate these new circumstances, he said. But widespread use of autonomous systems doesn't have to be destabilizing, he maintained.
Much drone work involves surveillance, he said, and by closely watching an adversary, one has more data to consider when deciding whether or not a certain action should be considered threatening.