confront 为及物动词，有不同的语义。例如《韦氏高阶》

a : to deal with (something, such as a problem or danger)

• Firemen regularly confront danger.

• They confronted [=(more commonly) encountered] many obstacles along the way.

c :to be a problem for (someone or something)

• We know of the financial problems confronting [=facing] local schools.

The problem confronting us today中，confront 为to be a problem for的意思。

which the nation confronted中，confront为to deal with 的意思。

所以，我们可以说：

Many problems confront us.

也可以说，We confront many problems.

that which= 融合型关系代词what。本句中that=the problem，the为前照应特指，即后面的限制性定语从句明确problem的所指。