なくしては

1. 1Without X, the result cannot be achieved; X is an essential condition.Ex. 1
2. 2Credits someone or something as indispensable to an outcome that has already happened.Ex. 2

A formal, mainly written expression found in speeches, essays, acknowledgments and editorials. It often conveys strong conviction or gratitude, as when thanking people whose effort made a success possible. It is stiffer and more emphatic than everyday ways of stating a necessary condition.

• 1.
  なくしてN1「なくして」 omits 「は」 but means the same, with a slightly flatter tone. Besides attaching to nouns, when the first clause is an action it can also take 「動詞辞書形＋ことなくして」. Both are written-style, the second clause is usually negative or expresses impossibility, and in most cases they are interchangeable.
• 2.
  〜ないことにはN3「〜ないことには」 likewise stresses a necessary prerequisite, but it can attach to verbs, adjectives, and 「名詞＋でない」, with a neutral register; it emphasizes that 'without doing it first, nothing can even be discussed'. 「なくしては」 attaches to nouns, is formal and written-style, and often carries a sigh of emotion or gratitude.
• 3.
  あってのN1「あっての」 states it affirmatively from the positive side—'only with A is B possible'—using 「名詞＋あっての＋名詞」 to directly modify the following noun, and often ends the sentence as 「AあってのBだ」; its register is neutral and it works in everyday speech too. The meaning is close, but the sentence structure differs, so rewriting is required.
• 4.
  なしにN2「なしに」 can also mean 'doing something without going through...' (e.g., 「断りなしに」), which 「なくしては」 cannot. When expressing a necessary condition, 「なしには」 is interchangeable with it, but 「なくしては」 is more written-style and more formal in tone.
• 5.
  ことなしにN1「ことなしに」 attaches to the dictionary form of a verb, while 「なくしては」 attaches to nouns, so they cannot be directly swapped. The two are close in the sense of 'without doing the first clause, the second cannot be realized', but 「ことなしに」 can also simply mean 'doing... without doing...'.

なくして is basically the same as なくしては, but adding は makes the emphasis on the prerequisite more pronounced; 〜ないことには usually attaches to verbs, is more colloquial, and likewise leads to a negative outcome; あっての emphasizes the prerequisite in an affirmative 'only with A is B possible' form; なしに and ことなしに focus on 'doing B without doing A' or 'doing B in a state without A', where the second clause is not necessarily negative or an expression of impossibility.