Theresa May has warned the Army's newest officer recruits that challenges posed by terrorist groups and changing international alliances have made the world more complex than ever before.
Speaking as the Queen's representative at the Sovereign's Parade at Sandhurst Academy, the Prime Minister referenced Khalid Masood's deadly attack in Westminster last month.
She also commended former Sandhurst graduate Captain Michael Crofts for tending to the wounded as the day unfolded.
Mrs May said she wanted Britain to build a "new and deep special partnership" with the European Union as the UK enters into negotiations to leave the bloc following the EU referendum last June.
She said: "The world into which you all now enter is also very different from that which confronted many of your predecessors.
"The threats we face today are more complex than ever before. And the missions that you will be asked to undertake will be similarly complex."
Mrs May said the importance of the armed forces remained paramount for keeping Britain safe, "whether it is the Royal Air Force flying missions against Daesh over the skies of Syria and Iraq, the Royal Navy protecting our sea lanes in the Gulf, or the British Army playing a leading role in UN peacekeeping missions in Somalia and South Sudan".
The Prime Minister also restated her commitment to meeting Nato's requirements for investing 2% of Britain's GDP in the armed forces, and promised to do "everything possible" to support military families.
Her reference to RAF missions against Daesh insurgents comes amid heated international discussions over the future of Syria's leadership following a suspected chemical weapons attack by Bashar Assad's regime on April 4.
MPs previously voted not to intervene in the conflict, which entered its sixth year in February.
Sandhurst trains the Army's officers and has previously hosted many famous graduates and members of the Royal Family, including Prince William and Prince Harry in 2005/06.
Other famous cadets who have passed out there include the Sultan of Brunei, Sir Winston Churchill, fascist Sir Oswald Mosley, James Bond author Ian Fleming and actor David Niven.