The island lies between North America and Europe and sits along important Arctic and North Atlantic routes.
Its geographic position makes it relevant to missile warning, aerospace surveillance, maritime security and the defense of North America.
During World War II, the United States established a military presence in Greenland after Denmark was occupied by Nazi Germany.
During the Cold War, Greenland became an important part of America's early-warning system.
That strategic role continues today.
The United States operates Pituffik Space Base in northwestern Greenland.
The installation supports missile warning, missile defense and space surveillance operations for the United States and NATO.
The base's location makes it particularly important for monitoring activity across the Arctic and the North Atlantic.
The new agreement builds on that existing military relationship rather than creating American access from scratch.
That is one of the most important pieces of context surrounding Trump's announcement.
The United States already has substantial military rights in Greenland.
The 1951 Defense Agreement
American military access to Greenland is rooted in a 1951 treaty between the United States and Denmark.
That agreement was negotiated at a time when the Cold War was intensifying.
Washington viewed Greenland as strategically important to the defense of North America and the North Atlantic.
The treaty provided the United States with significant military rights.
Those rights helped establish the foundation for American operations that eventually evolved into today's Pituffik Space Base.
According to Reuters, the United States already possesses extensive overflight and basing rights under the existing arrangement.
The new agreement therefore appears to strengthen and potentially expand an existing framework rather than create an entirely new American military relationship with Greenland.
The exact scope of the expansion remains one of the most important unanswered questions.
What "Permanent Control" Actually Means
Trump's phrase "permanent control over security" is likely to generate considerable debate.
Taken agreement would give the United States permanent access, basing and overflight rights and would remain applicable even if Greenland eventually became independent. literally, the phrase sounds like the United States has acquired sovereign authority over Greenland.
But that is not what Denmark and Greenland are saying.
The agreement does not make Greenland a U.S. territory.
It does not eliminate Danish sovereignty.
It does not make Greenland part of the United States.
And it does not appear to transfer control over Greenland's government to Washington.
Instead, the available information points toward a much broader American security role.
Reuters reported that the proposed agreement would give the United States permanent access, basing and overflight rights and would remain applicable even if Greenland eventually became independent.
That last point could prove especially significant.
Greenland has an established independence movement.
If the island were eventually to become independent from Denmark, the agreement could potentially continue to govern American military access.
That would give the United States a long-term strategic relationship with Greenland regardless of future constitutional changes.
But the exact legal mechanisms have not yet been fully disclosed.
Keeping China and Russia Out
One of the clearest elements of the agreement concerns America's strategic competitors.
According to a U.S. State Department official cited by AP, the arrangement would prevent non-NATO countries from establishing military bases in Greenland and restrict certain sensitive investments.
China and Russia are specifically identified as countries that would be prevented from establishing bases on the island.
The rationale is straightforward.
Washington does not want a strategic competitor establishing a military foothold in Greenland.
The Arctic has become increasingly important to Russia.
China has also expanded its economic and scientific interest in the Arctic in recent years.
From Washington's perspective, preventing a rival military presence near North America is a major security objective.
Secretary of State Marco Rubio characterized the agreement as permanently addressing U.S. national-security concerns regarding Greenland.
He said Greenland would remain part of the strategic defense area of North America and that adversaries would be excluded from the island and surrounding area.
That is one reason the agreement could be significant even without a transfer of territory.
The United States does not necessarily need to own Greenland to prevent a hostile power from establishing a military base there.
A long-term security agreement can accomplish much of the same strategic objective.
Military Expansion Could Be the Biggest Change
Trump's announcement also points toward a larger American military footprint.
He said the United States would immediately begin the process of developing a large military presence in Greenland.
That could mean additional infrastructure, personnel, radar capabilities, logistics facilities or other military installations.
However, the precise scale remains unclear.
Reuters reported that it was not yet clear whether new American bases would actually be constructed.