What legal steps would the U.S. Congress need to take to annex foreign territory like Greenland?
Executive summary
To annex a foreign territory such as Greenland under U.S. law, Congress would need to legislate the political status of that land after it had lawfully become U.S. territory—most plausibly via a treaty of cession or purchase negotiated by the President and ratified by the Senate—or by statute implementing a prior treaty; unilateral domestic legislation alone cannot lawfully convert foreign sovereign land into U.S. territory without an international cession or acquiescence [1] [2] [3]. Any attempt to seize foreign land by force would raise acute international-law prohibitions and political consequences even if the U.S. domestic branches tried to normalize the act [3] [2].
1. The prerequisite: acquisition under international law, usually a treaty
Historically the United States acquired foreign lands through treaties or purchases—Texas, the Louisiana Purchase, Alaska and the Mexican cessions are all tied to negotiated instruments or war settlements—because the Constitution vests treaty-making in the President with Senate advice and consent, and such instruments have been the standard route for cession [4] [5] [1]. Legal commentators and precedent treat treaty cession or voluntary transfer by the foreign sovereign as the legitimate path; Newsweek’s reporting echoes experts who say the U.S. “couldn’t make a move like this without the approval of the Danes” [2] [1].
2. Congress’s role once territory is acquired: disposal, rules, and potential admission
Article IV empowers Congress to “dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States,” so Congress has broad post-acquisition authority to govern a newly acquired territory and to set the pathway to statehood or other status by statute [6] [7]. The Library of Congress and CRS materials confirm any change in political status, including admission to the Union, requires congressional approval via statute [7] [8].
3. Two procedural tracks: treaty then statute, or joint resolution tied to cession
Practically, the United States has used both treaties of cession and congressional joint resolutions in different eras (Texas annexation used a joint resolution that conditioned admission on agreement with the foreign government, while other acquisitions used treaties) and Congress can legislate implementing measures for treaties that cede territory [9] [4] [1]. Legal scholars note Congress often follows a multi-step practice: negotiation by the executive, Senate ratification of a treaty (when required), then enabling legislation or appropriation to implement transfer and governance [1] [6].
4. Constitutional and doctrinal limits within U.S. law
There is debate about whether the Constitution enumerates a specific “annexation” power; some commentators argue Article I’s enumerated powers are domestic and that international cession practices have filled the gap historically, while Supreme Court doctrine (e.g., the Insular Cases and Downes v. Bidwell) recognizes Congress’s plenary power to determine how constitutional protections apply in newly acquired territories—meaning Congress controls incorporation and the timing of full constitutional application [10] [11]. That plenary power, however, operates after lawful acquisition and does not authorize the forcible seizure of foreign land without treaty or consent [11] [3].
5. International law and political reality: legality vs. capability
Annexation by force is broadly prohibited under modern international law and can be characterized as an act of aggression; illegitimate annexations remain disputed and can leave territory “occupied and illegally annexed,” with long-term diplomatic, economic and security costs [3]. Even if an act of annexation were decreed domestically, recognition by other states and institutions matters; the U.S. could attempt to legislate admission or incorporation, but that would not erase international illegality or the diplomatic break with the former sovereign [3] [2].
6. Practical roadmap Congress would need to enact
In short, the plausible legal steps for Congress are: accept a lawful cession or purchase (a treaty ratified by the Senate or an agreed framework), pass implementing statutes recognizing U.S. sovereignty over the ceded land and setting governance rules under the Property Clause, and—if desired—pass additional legislation admitting the area as a state under the Admissions Clause, mindful of precedents and any consent requirements when territory is carved from existing states [1] [6] [7]. Where reporting is silent, this account does not assert what tactics a foreign government would accept or how other states would respond; those are political facts beyond the domestic legal steps enumerated here.