What events happened in 1898 that were important to US foreign policy?

I assume that you are asking what happened in 1898 that
had to do with foreign policy in the US.  I have changed your question to reflect
this.

The most important thing that happened in 1898 was
the Spanish American War.  The Spanish American War was important for the United States
because it gave the US a world-wide empire.  After this war, the US controlled
territories as far away as the Philippine Islands.  This meant that the US had a way to
project power far away from its home territory.  It also meant that US foreign policy
would need to take into account events thousands of miles away from the US.  This led,
for example, to the fact that the US had to worry about Japan's actions in Asia in the
time leading up to World War II,.