The Daily National Intelligencer's front page is dominated by diplomatic correspondence surrounding the Mexican War, specifically focusing on John Slidell's failed mission as U.S. Envoy to Mexico in late 1845. Slidell's lengthy dispatches detail his humiliating rejection by Mexican Foreign Minister Peña y Peña, who refused to receive him as a legitimate diplomatic representative. The core dispute centers on credentials: Mexico claimed the U.S. had proposed treating only on the isolated question of Texas, while Slidell insisted he was commissioned to negotiate "all questions in dispute" between the nations. The Mexican government's refusal came amid internal chaos—General Paredes was leading a military revolt from the Texas frontier, the regular government under President Herrera was crumbling, and political factions (Federalists versus Centralists) were tearing the nation apart. Slidell's correspondence is remarkably candid about Mexico's instability: internal revolutionists were being arrested, the press was suspended, and he himself planned to withdraw to Jalapa to avoid being mistaken as an instigator of the brewing civil unrest. The subtext is chilling: Slidell warns that after the dust settles from Mexico's inevitable internal collapse, no future American negotiation will succeed without Mexico formally retracting its rejection—otherwise, "the Mexican people shall be convinced, by hostile demonstrations, that our differences must be settled promptly either by negotiation or the sword."

This June 1845 dispatch marks a critical turning point toward the Mexican-American War, which would formally begin just weeks after this newspaper went to press. The U.S. was intent on acquiring Mexican territories—particularly Texas (annexed in 1845) and the vast southwestern lands (New Mexico, California, Utah). Slidell's mission represented Washington's last serious diplomatic attempt to resolve these territorial disputes peacefully, or at least to purchase them outright. His failure and Mexico's internal chaos created the conditions for military conflict. This war would ultimately result in the U.S. gaining nearly half of Mexico's territory, fundamentally reshaping the North American continent and accelerating sectional tensions over slavery's expansion into new states—a conflict that would explode into civil war just 15 years later. What readers of June 1845 were witnessing was the moment diplomacy definitively failed and military inevitability became clear.

• Slidell explicitly mentions disputed 'instalments' (payments) between the nations that were in arrears—a detail suggesting Mexico owed the U.S. money, adding financial grievance to territorial disputes.
• The paper notes that Mexico's revolutionary force was stationed at the 'Rio del Norte' (Rio Grande)—exactly the border dispute that would trigger the first shots of war weeks later when U.S. troops clashed with Mexican forces over territorial claims.
• Slidell reports that General Almonte, a prominent Mexican politician, was in hiding with arrest orders issued against him—Almonte would emerge as a key Mexican military figure during the coming war.
• The correspondence reveals Mexico had granted 'extraordinary powers for six months' to President Herrera, suspended press liberty, and declared Mexico City 'in a state of siege'—showing a government in existential crisis, not a nation capable of coherent diplomacy.
• Slidell's stated decision to relocate to Jalapa 'to avoid suspicion of interference' reveals the depth of Mexican paranoia and internal strife—the U.S. minister couldn't safely remain in the capital without being accused of meddling in factions.

• John Slidell, the rejected envoy, later became a Confederate diplomat and senator—he would be captured in 1861 aboard the British ship Trent, nearly triggering British intervention in the Civil War, making this 1845 rejection a historical callback to his controversial later career.
• Slidell notes that some Mexican Centralists were advocating for the establishment of a 'monarchy in the person of some foreign prince, guaranteed by leading European Powers'—a scheme that would actually materialize in 1864 when France installed the Austrian Archduke Maximilian as Emperor of Mexico.
• General Paredes, the military officer defying orders from the Texas frontier, would indeed overthrow President Herrera just months after this dispatch—validating Slidell's prediction that 'the Government must succumb.'
• The newspaper itself cost $10/year for the daily edition ($6 for country subscribers)—equivalent to roughly $300 in modern money, placing serious news literacy firmly in the hands of the affluent and educated classes.
• Slidell's labored, diplomatic language throughout—his insistence on 'forbearance' and refusal to respond with 'menace and recrimination'—reflects how thin the ice of U.S.-Mexico relations truly was; any aggressive diplomatic move, he fears, would make 'war inevitable,' yet war was coming anyway.