、。
Well, Japan went through its own period of isolation too, after all.
Literal
Well, Japan [too-も] national-isolation was-doing [reason-わけ] [copula-だ] [and-し] [soft-なあ].
鎖国 (literally 'chain country') is the historical term for Japan's Edo-period policy of national seclusion (roughly 1633–1853). ~わけだし frames the preceding as a reason that's being stacked onto others ('and it's the case that X, too...'). The sentence-final なあ is a reflective/musing softener, the speaker talking half to themselves. The も after 日本 implies comparison with some other country or case presumably raised in prior context.