With an ongoing trade war between the United States and China, Russian military posturing in Eastern Europe at its greatest since the Cold War and the most unpredictable US administration in living memory, 2019 may offer no shortage of strategic surprises.
Here are some of the key areas to watch in the coming 12 months.
A new "big three" meeting?
With all the attention in Washington on the government shutdown and disputes over border funding, Trump has said little more on his December tweet that seemed to advocate a three-way conference with Russian President Vladimir Putin and Chinese counterpart Xi Jinping. Such a meeting, the president suggested, might offer the opportunity to stem a major global arms race. What worries America's allies - and many in the national security community - is that any such meeting might yield a "grand bargain" in which Trump listens to his most isolationist instincts and agrees to a US military pullback.
The first real indicator as to whether a Trump-Putin-Xi summit might happen will likely come in January, when US and Chinese trade teams meet in an attempt to de-escalate a growing dispute on tariffs. When Trump met Xi at the G20 in December, Trump agreed to waive new tariffs for 90 days. But time is now running out, and if such problems cannot be resolved, a broader meeting would feel all but impossible in the near future.
Europe - particularly Ukraine
European states have been particularly dismayed by Mattis' resignation, and are now worried Trump may double-down on his rhetoric that Europe has done too little for its own defense. That shouldn't stop US forces from continuing to be heavily involved in NATO exercises, however - at least unless Trump directly orders them to.
Europe's multiple political crises will continue to swirl. If Britain is to avoid a chaotic "no deal" Brexit in March, it will now have to be through a last-minute agreement. French President Emmanuel Macron may have blunted December's "yellow vests" protests somewhat by giving in to many of the demonstrators' demands, but he is likely to face further confrontations with an increasingly angry populace. European parliamentary elections in May will likely see a strong showing by right-wing populist parties. German politics will remain volatile ahead of the departure of Chancellor Angela Merkel, as will those in Italy - now widely regarded as the most vulnerable nation in the euro zone.
The most likely venue for escalating conflict, however, remains Ukraine. Having now enclosed the seized Crimean peninsula with a fence and taken control of the entrance to the shared Azov Sea with a bridge, some now suspect Moscow may attempt another limited land grab, perhaps towards the Ukrainian coastal port of Mariupol. Whether that comes or not, increased posturing by NATO and Russian forces alike in the nearby Black Sea also feels inevitable, particularly ahead of Ukrainian elections on March 31.
South China Sea
While much of the meat of China's confrontations with the West comes from the trade dispute and associated issues such as the detention of a Huawei executive in Canada, Beijing's ambitions may play out most visibly in the South China Sea.
Despite a UN court ruling dismissing its maritime claims, Beijing will continue to build military bases on artificial islands across the South China Sea, while US warships and regional allies will continue to challenge them with so-called Freedom of Navigation Operations.