How can nation's

problems

affect

another?

Answer:The results of the Peace of Westphalia have not always been pretty. After Hitler took power and before World War II broke out, Germany's persecution of its Jewish population was implicitly acknowledged by the United States, and (as far as I know) by all other nations as well, to be Germany's business, and not a casus belli. The most dramatic post-World War II example of that kind of hands-offness was the refusal by the United States to intervene in the Rwandan genocide of 1994, when, in the midst of a civil war between Hutus and Tutsis, the dominant ethnic groups in Rwanda, the Hutu population in a period of about 100 days killed between 500,00 and 1 million Tutsis, before being decisively defeated by the Tutsis. The Hutus were armed mainly with machetes, and the United States could have prevented the genocide with modest military means and little risk, but, in keeping with the Peace of Westphalia (though I don't think that was ever mentioned), did nothing.