International comity in taxation; reasons

A practice of showing courtesy among nations. It occurs when one country shows respect for the laws, judicial decisions, and institutions of another. (International Comity. Definition. www.quimbee.com)

Comity is the respect accorded by nations to each other because they are sovereign equals. Thus, the property or income of a foreign state or government may not be the subject of taxation by another state. The following are reasons for international comity in taxation.

[1] Par in parem non habet imperium. As between equals, there can be no sovereign. One state cannot exercise its sovereign powers over another. This is the doctrine of sovereign equality.

Par in parem non habet imperium (Latin for "equals have no sovereignty over each other") is a general principle of international law, forming the basis of state immunity. Because of this principle, a sovereign state cannot exercise jurisdiction over another sovereign state. (en.wikipedia.org)

[2] Immunity from suit. A foreign government may not be sued without its consent. (Holy See v. Rosario) Therefore, it becaomes useless to impose a tax which cannot be collected.

Sovereign immunity, or crown immunity, is a legal doctrine by which the sovereign or state cannot commit a legal wrong and is immune from civil suit or criminal prosecution, strictly speaking in modern texts in its own courts. A similar, stronger rule as regards foreign courts is named state immunity. (Sovereign immunity - Wikipedia. en.wikipedia.org)

[3] International usage or customary international law. There is understanding among states that when a foreign sovereign enters the territorial jurisdiction of another, the former does not intend to degrade its dignity by placing itself under the jurisdiction of the other. There is no intent to go down to the level of an individual.