化 attaches to an established base to name a change or conversion. The resulting word is a noun, and adding する makes it a verb meaning either “become” or “make into,” depending on the word and sentence.
Packaging a change as a concept
This suffix turns a base into the name of a process or its result. For example, 少子化 treats a declining birthrate as a recognized social development, while 効率化 presents making something more efficient as a defined process. This compact, concept-like quality explains why such words are frequent in informational writing.
Noun and verb uses
The form without する is a noun. With する, it describes the change as an event.
少子化への対策が必要だ。
Measures addressing the declining birthrate are necessary.
Here させる clearly presents the policy changes as the cause.
Direct description versus packaged transformation
複雑になった directly says that something became complicated. 複雑化した packages the same general development as “increasing complexity” or “complication,” so it often suits analytical or institutional descriptions better. The two forms can describe related situations, but they are not automatically interchangeable.
担当者が増えて、連絡方法が複雑になった。
As more people became responsible, the way of communicating became complicated.
