The United States entered World War I because . a. of German aggressions against British ships and the Zimmermann Telegram b. Pancho Villa invaded American soil with thousands of militia c. during the Lincoln County War, the United States lost a portion of New Mexico that it needed to regain to expand the railroad d. so many young men had enlisted and propaganda had convinced every American household that war was a necessity

a. Of German aggressions against British ships and the Zimmermann Telegram.

Explanation:

At the start of the First World War, the United States was just a neutral nation, with no sides. The country stayed neutral till 1917 when it was 'forced' to defend itself from Germany’s ever-increasing aggressive nature against its (US) nationalities.

Under the presidency of Wilson, the United States remained a neutral nation amidst the rising tension and war between the major powers in Europe. But when tensions escalated and the Germans attacked the merchant vessels of the United States killing more than a hundred Americans in the sinking of the British passenger ship Lusitania.

Moreover, the Zimmermann Telegram which reveals Germany's promise of giving Texas, Arizona and New Mexico to Mexico if they (Mexico) side with Germany in the war led to the decision to join the War on the side of the Allied powers which included the United Kingdom, Russia, and France.

Thus, the correct answer is option a.  

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