One hundred years ago on Thursday, the United States entered the first world war, a bloodbath prompted by unchecked global instability and a series of flashpoint events that leaders allowed to spiral out of control. Today, the world sits at a similar precipice. Americans should keep the historical precedents in mind while evaluating Thursday night's U.S. cruise-missile attack on Syria's Shayrat air base.

President Donald Trump was correct to order the bombing. Syrian President Bashar Assad has flaunted international law, including the use of chemical weapons against his own people. Minimal consequences resulted from an earlier chemical attack in 2013. Then-President Barack Obama only succeeded in emboldening Assad with his tepid response.

But Trump's administration further emboldened Assad last week by suggesting that the dictator was here to stay and that his fate was up to the Syrian people to decide. Assad's chemical attack quickly followed. He should never have been allowed to feel safe, much less escape severe consequences in 2013.

Today's situation is far more complicated. Russian-supplied warplanes, including the ones that launched last week's chemical attack, were based at Shayrat. Senior U.S. officials say there are signs of potential Russian complicity in the attack. Russia accused Washington of a "flagrant violation" of international law and withdrew from an information-sharing agreement with Washington designed to avoid inadvertent clashes between the two countries' forces in Syria.

Tension was already high because of Russian attempts to manipulate the Nov. 8 presidential election. The threat of two nuclear superpowers entering direct military confrontation has escalated.

That's just one international flashpoint.

Nuclear-armed North Korea has been launching increasingly powerful ballistic missiles designed to intimidate Japan and South Korea while warning it is at the brink of war with the United States. Ahead of his summit with Chinese President Xi Jinping, Trump warned: "If China is not going to solve North Korea, we will."

Meanwhile, China is projecting greater naval and air power into the South China Sea. The Philippines has sent a warship to defy Chinese assertions of territorial sovereignty. U.S. and Chinese naval vessels have engaged in cat-and-mouse confrontations. Again, two nuclear superpowers are staring each other down.

When the Soviet Union and America stood at the brink of war during the Cuban missile crisis, President John F. Kennedy gave his staffers copies of "The Guns of August," Barbara Tuchman's 1962 book about the miscalculations and bellicosity that sparked World War I. Trump might consider reading it himself.

His attack on Syria was an act of war. Trump has not sought congressional approval, nor clearly articulated a strategy or stated whether his goal is to oust Assad once and for all.

World War I serves as a monument to the consequences when emotions and egos dominate over cool-headed deliberations. Lest the mistakes of 1917 be repeated, Trump owes it to his country to bring Congress into the loop.

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