OK, thanks.
It could just be that your history and caches are quite large. You can clear just history by clicking History > Show All History, select all, and press Delete. You can clear history using Safari > Clear History... > Clear: all history, but that clears history, cookies, etc. on all devices logged into your iCloud account. You may have to log back into website you use, so make sure you know your website usernames and passwords before using this option.
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