Companies are (effectively) nationalised during wartime. There isn't much in history to indicate how war would affect multinational companies.
During WW2, a number of American companies (i.e. Ford) supplied Nazi Germany, France and Russia with parts. Obviously war is good for business when you are neutral.
However, France fell immediately. The British were self sufficient - so there is no guidance here except that French factories had compatible parts and could be adapted instantly to German needs.
Broken Russian tanks (with American parts) were easilly pressed into service by Germans. Nazis could not do the same with British tanks because the parts were incompatible.
This economic connection to Germany has been cited by some as the cause of delay in American intervention.
There is nothing in more recent times. The UK-US international corporations are so intertwined that they cannot now be seperated. National Grid in the USA is a British company. BAE (formerly British Aerospace, formerly Hawker) power nearly all electronics in the USAF.
What would happen if the UK and USA went to war? They have been supplying each other with technology for so long that they find pressing the fire buttons on each other causes a protection fault and system shutdown
Ok, I am exagerating, but there are huge economic forces at play and we have no way of knowing the true effects of nationalising companies which are so globalised in their operations.