Learn Arabic (Modern Standard): الإقليمان كلاهما شبه مستقلين.

Normally, 'independent' would be the predicate of this nominal sentence and take the nominative dual ending (مستقلان). However, the word شبه ('semi-') forms an Idafa (genitive construction) with the word that follows it. Because it is the second part of the Idafa, it must be in the genitive case, which is مستقلين for the dual.

If مستقلين is in the genitive case, what is the actual predicate of this sentence?

Syntactically, the word شبه itself is the predicate. Because it acts as the predicate, it takes the nominative case marker (شبهُ). You can think of the literal grammatical structure as: 'The two territories are a semi-[entity] of two independent [ones].'

Does the noun after شبه always have to agree in number and gender with the subject?

Yes. Even though it is grammatically trapped in a genitive Idafa, its logical purpose is still to describe the subject. Since the subject الإقليمان is dual masculine, the word following شبه must also be dual masculine. If the subject were singular feminine, for example, it would be شبه مستقلة.

Why does the word كلاهما ('both of them') use an alif in this sentence?