how to find trigger for the below action i explained?

My question is scenario. I have one standard object , name account . I have two fields -

one is country - list of values

second one is state - dynamic choice list

if we select a value from country , e.g united states as a country , then automatically state field comes up on a page. - like there must be some page layout level condition for field to pop -up.

but at page layout level , I cannot find both of the fields , neither the configuration / conditions(I am checking correct layout and i have verified that)

consider that these are standard fields , and can anyone tell me how to search for the condition/trigger or anything which is causing this action of field is popping up when country is selected as united states ?