WEST POINT, N.Y. – President Obama outlined a new national security strategy rooted in diplomatic engagement and international alliances on Saturday as he repudiated his predecessor’s emphasis on unilateral American power and the right to wage preemptive war.

Eight years after President George W. Bush came to the United States Military Academy to set a new course for American security in the aftermath of the Sept. 11 attacks, Mr. Obama used the same setting to offer a revised doctrine, one that vowed no retreat against American enemies while seeking “national renewal and global leadership.”

WARSAW, Poland — Polish President Lech Kaczynski, who died Saturday in a plane crash in Russia, was a one-time anti-communist activist who teamed up with his twin brother to take his country in a nationalist, conservative direction.

Kaczynski, 60, pursued a strongly pro-U.S. line in foreign relations, in accordance with a cross-party consensus that has grown in Poland since the fall of communism. He was an enthusiastic backer of plans to site a U.S. missile defense facility in the country, the largest of the European Union's new eastern members.

However, the prickly nationalism of Kaczynski and his identical twin brother, Jaroslaw — who served for a time as prime minister and is now opposition leader — sometimes complicated ties with European neighbors and Russia.

The president, for example, long held out against the EU's so-called Lisbon reform treaty before signing it last November. Still, his appeal at home rested partly on his forthright representation of Polish views and his tough stance on law and order.