Is it permissible under international law to militarily attack a country/region if it's conducting a total blockade, including of foodstuff?

Question

Tigray (TDF) regional authorities say they are now attacking the neighboring Amara and Afar regions (which have different regional governments under Ethiopia's federal constitution) because Tigray needs to open a communications/trade route to allow aid in, which is blockaded by the federal government forces and their regional allies.

Getachew confirmed that the Tigray forces’ aim in the Afar region is to control a crucial supply line to the rest of Ethiopia from neighboring Djibouti, on a major shipping lane. He called it “part of the game,” saying people in Tigray are starving.

The UN seems to confirm that Tigray is under [near-]total blockade from the Ethiopian government, including of UN humanitarian aid--as the BBC relates:

The UN says no trucks carrying provisions have entered Tigray via this route since 22 August, and none with food aid since 20 August.

An estimated 172 trucks are now stuck at Semera, the regional capital of the Afar region.

The UN says 100 trucks a day need to cross into Tigray to meet the needs there.

However, since mid-July, only 335 trucks have made it into the region, which is less tha[n] 10% of the aid supply needed.

To the south, pro-government forces in the Amhara region have been preventing supplies from getting through.

It's also been impossible to bring in aid by road from Sudan, into western Tigray, an area under the control of groups supporting the Ethiopian government.

And now, with the route via the Afar region severely restricted, the problem has become particularly acute.

This level of blockade itself may be a war crime, but is it justifiable under international law to attack a neighboring country/region in such circumstances?

Answer 1

International law generally prefers not to get involved in civil wars, which this is. Regardless, international law is customary rather than statutory, because there is no single entity with general powers of enforcement against states which violate it. Saying that something is "against" international law is, by itself, largely meaningless, except perhaps in some specialized forums such as the International Court of Justice or the World Trade Organization. What matters is what other countries will do about it.

There are a number of possible responses that the international community can take to internal conflicts like this:

• Ignore it, and assume that it's the individual country's problem. This is the "default" response, particularly in cases where the national government is still functional and still has de facto control over a large portion of its territory. Individual allies may render aid to the country in accordance with treaties or other agreements, but usually only if asked. Humanitarian aid will (or should) also be provided in most cases, especially if civilians have been harmed or displaced by the conflict.
  • In this particular case, it might not be possible to provide humanitarian aid without first resolving the conflict. Humanitarian organizations such as the Red Cross specifically forswear the use of violence, and must not participate in the conflict themselves. In return, they are accorded special status, and must not be fired upon. "Participation" includes providing arms or materiel to either side, which the Foreign Affairs minister has accused unspecified organizations of doing. If true, that is a grave accusation which complicates matters considerably. If false, it's a dangerous lie, which also complicates matters considerably. Regardless, allowing humanitarian aid through is generally expected by international law and custom, but there's no specific remedy for refusing to do it.
• Recognize one side as the legitimate government (or government-in-exile) of the country, and refuse to diplomatically acknowledge the other. If the "illegitimate" side is winning, this may lead to sanctions or other measures, but direct military intervention is normally avoided. Indirect military aid (arms, materiel, etc.) may or may not be provided depending on the circumstances.
• Recognize one side as legitimate, but maintain informal diplomatic relations with the other side. This is the way many countries, particularly the US, interact with Taiwan.
• Invade and occupy the country and try to sort things out yourself. This is regarded as a last resort, and is generally only seen as acceptable if the "illegitimate" side of the conflict is a credible threat to the international order or to the safety of your own civilians (e.g. ISIL). Rarely, a country might intervene for strategic reasons, but that is usually frowned upon.

TL;DR: "International law" does not normally become relevant for this sort of situation. Humanitarian organizations do have special status in times and places of conflict, and international law does generally expect that status to be respected, but it's difficult to enforce in this context.