ならでは is a construction which indicates that something is 'unique to (A)', or 'impossible if not (A)'. While
ならでは is usually considered as its own standalone word, it is actually just a combination of the negative-
conjunctive form of the the classical copula なり, ならで, with the addition of the
adverbial particle は.
ならでは will follow nouns, and the sentence will then usually go on to say what the thing is that is unique to (A).
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味噌（みそ）カツは名古屋（なごや）ならではの食（た）べ物（もの）です。
Misokatsu is a food unique to Nagoya.
アメリカならではの観光地（かんこうち）といったらどこを連想（れんそう）しますか。
Where do you think is a tourist attraction that is unique to the States?
この祭（まつ）りはこの地域（ちいき）ならではの祭（まつ）りです。
This festival is unique to this area.
As seen in the above examples,
ならでは will only be used when something is being evaluated positively. As a result of this, it is very common to see in advertising and slogans.
ならでは may be seen directly before the
auxiliary verb だ. In these cases, the thing that is unique to (A) will have been expressed earlier in the sentence, or will be obvious from context.
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こんな綺麗（きれい）な作品（さくひん）を作（つく）れるのは、藤田（ふじた）さんならではだ。
Only you, Fujita-san, can create such an amazing piece.
車（くるま）なしで生活（せいかつ）できるのは都会（とかい）ならではだ。
Only in the city can one live without a car.
Based on the history of
ならでは, the structure being the negative-
conjunctive form of the copula なり means that it is basically identical in meaning of the more modern でなくては 'if it isn't (A)'.