As people convert from fiat over to cryptocurrency, raising its market cap on average $1,000,000,000 per day during the month of May, 2017 (surpassing Airbnb and Uber), the paradigm of war and how it is funded may end up changing.
https://themerkle.com/cryptocurrency-market-cap-reaches-77bn/
Wars have been funded historically via debts issued through a debt-based fiat currency system. The debts are repaid at a later date by the tax base of the populace, and funding in the present for warfare is allowed to far exceed current wealth or resources of the society.
In the case of the USA, the fiat currency used is the Federal Reserve Note. This is sometimes referred to as the Petro-Dollar. Wars are funded by borrowing against the future generations of Americans, and money is spent in the present that wouldn't otherwise exist.
Bitcoin, and cryptocurency in general, is not a debt-based money system. It is based on the actual coins owned at the time. If nation states switched (either voluntarily or through market forces) to cryptocurrencies war would be unaffordably expensive.
https://news.bitcoin.com/bitcoin-break-petrodollar-monopoly-peace/
Aside from the fundamental change in funding methods, usage of cryptocurrency would discourage war in one other way. That is the cost of those cheerleading for war would rise.
The person promoting or voting in favor of war would have an immediate bill serving as a strong disincentive for them to send others off to their possible death.
A world with less war has many advantages, and among them include areas that would've been bombed having a chance to develop. In theory, everyone would be a winner. Similar to those investing in Bitcoin this month.
Can bitcoin even be taxed? Can a government know what you have in cryptocurrency or what you buy with it? If they can't then cryptocurrency becomes a serious constraint on government excess of all types.
Bitcoin is already taxed as an asset like a commodity would be. A government can know by checking the publicly available blockchain to see each transaction, should they know how to use it. Crypto constrains government in that they can't print it.