Is there a link between national debt/trade deficit and starting a war?

I am rather skeptical of the theory that leaders go to war to get people's mind off debt, but it's certainly a discussionable matter. However, I do have an example for you of a debtor invading his creditor to write off the debt : here. Spoiler: it backfired rather spectacularly.

One proximate cause of World War II was the Versailles treaty, and the huge reparations debt it imposed on Germany. One of Hitler's main platform planks was to revitalize the German economy by "tearing up" that Treaty.

Under the Dawes Plan of 1928, Germany would have been paying off Versailles debt for 60 years, all the way to 1988, if it had not been wiped out by World War II.

It is sometimes argued, albeit farcically in the manner of "For the want of a horseshoe nail", that WWII was started over Germany's inability to deliver telegraph poles it owed to France and Belgium.

For the want of a telegraph pole, the Ruhr was occupied. For the want of a free Ruhr, a shaky economy was sent into a death spiral. For the want of a prosperous economy, the Weimar Republic was destabilized politically. For the want of a stable government, the Nazis were able to take over and start re-arming. For the want of a regime that wasn't evil, the world erupted into war. All for the want of a telegraph pole.

But this is less of a national debt issue than the Allies screwing themselves by burdening Germany with outrageous reparations demands, and then following through on collecting them by force. It convinced Germany of the need to re-arm, and gave the German people a smoldering hatred of the Allied Powers that allowed Hitler's broader war schemes to blossom.

Debt between sovereign states (or separate currency unions) is a peculiar creature.

We can take for example a late 1970s year in which Japan was pouring econo-cars into the US market, US car companies were in deep trouble, and it seemed like every VCR, TV, and eggbeater had a Japanese name on it. Due to the habit of Japanese not to buy foreign goods if they could avoid it, we had a trade imbalance, and this was 'funded' by 'borrowing money' from Japan. What this meant in particular is that the Japanese central bank would purchase US Treasury Bills, flooding the US and eventually global economy with Yen.

If we look carefully at what that means, it means that the US printed paper IOUs furiously while the Japanese poured their efforts into making 'real things': cars, TVs, etc., and shipping these to us to consume.

Japan currently holds about $1 trillion in US debt (China, at this moment, has about $1.3 trillion). If Japan sells this debt to Saudi Arabia, it would be most likely in exchange for oil - something 'real'. If Japan were to demand 'repayment', the only way that could be done is for Japan to purchase real goods from the US - aircraft, wheat, beef, oranges, CPU chips, lumber, or whatever. At that point, dollar denominated debt would be repatriated in exchange for dollar denominated products.

Needless to say, anything bought from America is not produced in Japan. Presumably anything the Japanese could produce would never be bought from the US. Therefore, Japan would be creating jobs in the US if they demanded 'repayment'. Probability this will happen: zero.

In short, if the US sells debt to foreign countries that 'protect' their domestic industries from foreign competition, they will tend to accumulate foreign debt which they will never redeem, unless they get in the kind of trouble where they need massive imports.

Another peculiarity of all this is that the Japanese have been big savers. Therefore, the combined debt of the Japanese government and the American government are 'assets' to Japanese households. These 'assets' tend to be kept under the mattress, figuratively speaking. In short, money is earned, much of it is stashed away and never spent.

One interpretation of what money is is that it stimulates production and consumption. Therefore, as the US spends money like water the restaurants are full of waiters pocketing tips that are using it to buy gasoline which the station uses to buy gas which the oil company uses to run refineries, etc., etc. If the wage earner chooses in instead to park it in a safe, it doesn't stimulate commerce. If it sits in the safe until the 20-something retires at age 55, that currency does not act as money over a period of, say 30 years. That is 30 years of potential vendors not working and not earning those yen or dollars.

Therefore, as the US 'prints' money and puts it in circulation, foreign debtors remove it by 'saving' it in their respective central banks. This is also a problem within the US: wealthy people also 'hoard' cash, so to speak, rather than keeping it circulating in the economy to stimulate further activity.