Even though this issue is usually settled diplomatically, there still remains a considerable amount of criticism to be faced.

diplomatically 是副词，由名词 diplomacy（外交）加上形容词后缀 -tic 变成形容词 diplomatic（外交的），再加上副词后缀 -ally 构成。意思是"通过外交手段地、在外交层面上地"。 这里 diplomatically 修饰动词 settled，表示"以和平协商的方式解决"。