GMAT Sentence Correction (SC) | The personal income tax did not become permanent in the United States

The personal income tax did not become permanent in the United States until the First World War; before that timethe federal government was dependent on tariffs to be their main source of revenue.

Issue:Structure | Verb tense

Analysis:
1. The sentence connects two independent clause using ";". For such structures, the second clause should be independent and follow from previous clause.
2. In the second clause the action "government was dependent on tariffs" occurs before
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