specialized
v.v. to focus your time and effort on one specific subject or skill. You do this when you want to become an expert in a particular area.
v. to concentrate one's efforts or interests on a particular area of study, business, or activity. Intransitive — requires a prepositional phrase to specify the field of focus.
She decided to specialize in international law.
After finishing medical school, he chose to specialize in pediatrics to help children in rural communities.
While general practitioners provide essential broad-spectrum care, many doctors eventually specialize in order to master the complex diagnostic tools and treatments required for specific chronic conditions.
The verb is intransitive and almost always takes the preposition 'in' before the subject of expertise.
He specialized international lawHe specialized in international lawThe verb is intransitive and requires the preposition 'in' to connect to the field of study.