Crossing Your Neighbor's Rubicon: A Look at Territorial Sovereignty and Necessity

• Pages: 231-266
• Date: 01 July 2025
• Published date: 01 July 2025
• Author: Matthew R. Sonn
• Subject Matter: Derecho Civil

Crossing Your Neighbor’s Rubicon: A Look at

Territorial Sovereignty and Necessity

Matthew R. Sonn*

ABSTRACT

In an era of global conf‌lict, states face the challenge of defending themselves

against threats that often originate far from their borders. This paper examines

the principle of necessity as a potential justif‌ication for violating the territorial

integrity of non-consenting states. By analyzing historical and contemporary

interpretations, the study delves into key concepts such as territorial integrity,

necessity, the constraints of the UN Charter, and jus cogens norms. It seeks to

clarify whether states can transit through a non-consenting state to address se-

curity threats. To address this complex issue, the paper proposes a framework

designed to ensure that such transit remains within legal bounds. This frame-

work will be tested through various hypothetical scenarios, demonstrating how

states can navigate the delicate balance between self-defense and respect for

sovereignty. Ultimately, this analysis aims to contribute to the ongoing dis-

course on state conduct in an increasingly interconnected and threatening

global landscape.

I. INTRODUCTION

Modern warfare has become more global. New technological developments

mean that weapon systems have longer ranges, are cheaper, and are more widely

available to an array of actors. This means that potential attacks and security

threats will come from state and non-state actors across wider spans of geography.

1

For example, in October 2023, Houthi rebels in Yemen launched drones and cruise missiles at

Israel that f‌lew from Yemen over the Red Sea and crossed into Egypt. Ahmed Mohamed Hassan & Dan

Williams, Drone Blasts Hit Two Egyptian Red Sea Towns, Israel Points to Houthi, REUTERS (Oct. 27,

2023, 5:19 AM), https://perma.cc/U8CE-5CWH; and DEF. INTEL.AGENCY, IRAN ENABLING HOUTHI

ATTACKS ACROSS THE MIDDLE EAST (Feb. 2024), https://perma.cc/P434-P2WW.

As such, states no longer face a threat from only those they share a border with,

but from other actors both regionally and globally. In planning to respond

* Commander, Judge Advocate General’s Corps, U.S. Navy. LL.M., 2024, Harvard Law School;

J.D., 2008, Loyola University New Orleans College of Law; B.S., 2005, Truman State University. This

article began life as a research paper submitted in partial fulf‌illment of the requirements of a Master of

Laws degree at Harvard Law School, funded through the Naval Postgraduate School’s civilian education

program. Many thanks to my advisor Professor Gabriella Blum, my writing group, and in particular my

classmates CDR Matthew Pekoske, USCG, and LCDR Sarah Padway, JAGC, USN, for the tremendous

feedback and insights. I also want to thank the editors at the Journal of National Security Law and Policy

for their insights and suggestions in making this a better article. Finally, I want to thank my wife Emily

for all of her help and support through this process. All opinions and views expressed in this article are

solely those of the author and do not ref‌lect the views of the Department of Defense or Department of

the Navy. © 2025, Matthew R. Sonn.

1.

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militarily, this will inevitably lead states to consider transiting through nearby

states in order to address these attacks and growing threats. Legal advisors to

these militaries should always advise their states to seek consent from the state

that has to be crossed, but this paper will examine what happens when those

states say “no.” Consider the 1981 strike by Israel on an Iraqi nuclear power

plant located in Osirak, Iraq. Israel claimed that the plant posed a “mortal dan-

ger” to their existence.

2

On This Day 1981: Israel Bombs Baghdad Nuclear Reactor, BBC NEWS, https://perma.cc/FK6E-NE43.

Israeli military aircraft f‌lew through Jordanian and Saudi

Arabian airspace, without their consent, to strike the plant inside of Iraq.

3

This

strike was condemned by the United Nations Security Council and was met with

great condemnation from states across the globe as an unjustif‌ied act of aggres-

sion.

4

But, interestingly, the issue of violating Jordanian and Saudi Arabian sov-

ereignty was largely ignored and was not addressed in the f‌inal resolutions.

A tremendous amount of ink has been spilled exploring a state’s right to defend

against attacks emanating from a non-state actor group located in the territory of

another state.

5

The so-called “unwilling/unable doctrine” that gained traction in

the aftermath of the terrorist attacks on September 11, 2001, and the subsequent

“Global War on Terrorism,” was taken up by a number of states to justify the use

of force against non-state actors located outside their borders. While it is still

debated, there are many who argue that a state is lawfully allowed to take kinetic

action against a non-state actor who is operating within the borders of another

state.

6

Logically, it seems to f‌low that if a state can legally conduct strikes within

the borders of a state, then merely transiting should also be permissible. This pa-

per will further interrogate this position below.

This paper will seek to investigate the relationship between the principles of

territorial sovereignty, necessity, and self-defense. In particular, this paper will

seek to address the question presented in a scenario in which a state, being threat-

ened or attacked by another state actor, must transit through the territory of a third

state in order to defend against the attack. Does the domain (e.g., land, sea, or air)

matter in this calculus? How do the principles of territorial sovereignty, necessity,

and self-defense interact, and how are they balanced when a neutral third-party is

implicated?

2.

3. Whitney Raas & Austin Long, Osirak Redux? Assessing Israeli Capabilities to Destroy Iranian

Nuclear Facilities, 31 INT’L SEC. 7, 11 (2007).

4. See S.C. Res 487 (June, 19 1981); U.N. SCOR 36th Sess., 2280th mtg., U.N. Doc. S/PV.2280 (June

12, 1981); U.N. SCOR 36th Sess., 2281th mtg., U.N. Doc. S/PV.2281 (June 13, 1981); U.N. SCOR 36th

Sess., 2282th mtg, U.N. Doc. S/PV.2282 (June 15, 1981); U.N. SCOR 36th Sess., 2283th mtg., U.N. Doc.

S/PV.2283 (June 15, 1981); U.N. SCOR 36th Sess., 2284th mtg., U.N. Doc. S/PV.2284 (June 16, 1981);

U.N. SCOR 36th Sess., 2285th mtg., U.N. Doc. S/PV.2285 (June 16, 1981); U.N. SCOR 36th Sess.,

2286th mtg., U.N. Doc. S/PV.2286 (June 17, 1981); U.N. SCOR 36th Sess., 2287th mtg., U.N. Doc.

S/PV.2287 (June 17, 1981); U.N. SCOR 36th Sess., 2288th mtg., U.N. Doc. S/PV.2288 (June 19, 1981).

5. See generally Ashley S. Deeks, Unwilling or Unable: Toward a Normative Framework for

Extraterritorial Self-Defense, 52 VA. J. INT’L L. 483, 486-88 (2012); Gabriella Blum & John C. P.

Goldberg, The Unable or Unable or Unwilling Doctrine: A View from Private Law, 63 HARV. INT’L L.J.

63 (2022), Louise Arimatsu, The Law of State Responsibility in Relation to Border Crossings: An

Ignored Legal Paradigm, 89 INT’L L. STUD. 21 (2013).

6. Deeks, supra note 5, at 486-88.

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To contextualize these issues, the following hypothetical scenarios spanning

the three major domains of warfare—air, land, and sea—will be employed.

7

All

of these scenarios involve the same basic factual premise: State A has suffered an

armed attack by State B, and State A intends to engage in self-defense under

Article 51 of the United Nations (hereinafter UN) Charter. State C is geographi-

cally located between States A and B and does not give consent to State A to enter

its territory.

Scenario 1 – Air. State A has determined that to address the armed attack from

State B, they must enter the airspace of State C. State A will launch cruise mis-

siles to strike a target in State B, and their f‌light path will overf‌ly State C, crossing

through their national airspace. State A will also f‌ly reconnaissance aircraft from

State A over State C in order to gather additional intelligence on the activities of

State B.

Scenario 2 – Land. State A determines that the only way to respond to State B

is to send their troops on land through State C to engage the forces of State B,

inside of State B. Due to State B’s air defense systems, State A would not be able

to f‌ly their troops into State B. In order to neutralize the threat from State B, State

A intends to traverse the land territory of State C to engage State B.

Scenario 3 – Maritime. State A intends to sail some of its naval vessels into the

territorial and internal waters of State C to land forces inside of State B. For

example, there is a river in State C whose mouth is within State C’s territorial

waters, but the river f‌lows into State B. State A intends to sail its vessels up the

river to land forces ashore inside of State B.

To address these questions this paper will proceed as follows. First, this paper

will look at territorial integrity generally and within the domains of the sea and

air while simultaneously examining the many statements made regarding cyber-

space that may shed light on views in the physical world. Next, the paper will pro-

ceed to interrogate the principle of necessity, starting with a historical overview

that proceeds into a look at the modern understanding of necessity as an excuse to

behavior that is otherwise wrongful under international law. The paper will then

look at the UN Charter and what is meant in Article 2(4)’s mention of territorial

integrity, the jus cogens norms of aggression and non-intervention, and jus ad

bellum. At the conclusion, the paper will suggest that, when certain conditions

are met, a state’s armed forces may transit through another state’s territory to

defend itself from a third state.

II. TERRITORIAL INTEGRITY

A. In General

To explore the issue of whether State A has the legal authority to enter the terri-

tory of State C in order to defend itself from State B, we must f‌irst explore the

7. While this paper will look at sovereignty ideas as they pertain to the cyber domain, these ideas will

not be explored in depth. Instead, those statements will be utilized to illuminate thoughts on sovereignty

and territorial integrity more generally.

2025] CROSSING YOUR NEIGHBOR’S RUBICON 233