China has spent nearly two decades building a digital wall between itself and the rest of the world, a one-way barrier designed to keep out foreign companies like Facebook and Google while allowing Chinese rivals to leave home and expand across the world.

Now President Trump is sealing up that wall from the other side.

Google said on Monday that it would limit the software services it provides to Huawei, the telecommunications giant, after a White House order last week restricted the Chinese company’s access to American technology. Google’s software powers Huawei’s smartphones, and its apps come preloaded on the devices Huawei sells around the world. Depending on how the White House’s order is carried out, that could come to a stop.

For Huawei, the big impact will be abroad, since Chinese customers already have limited access to Google’s services. Google’s move will have its biggest effect in places like Europe, where it has emerged as a big smartphone seller. Other companies will inevitably follow. In effect, the move puts pressure on Huawei’s international expansion dreams.

If China and the United States have begun a technological Cold War, then the Huawei order can best be seen as the beginnings of a digital Iron Curtain. In this potential vision of the future of technology, China will continue to keep out much of the world. The United States and many other countries, goes this thinking, will in turn block Chinese technology.