Complex sentence: Emancipation for Catholics was a core promise during the campaign for implementation of the Act of Union in 1801 but it was not until 1829 that the Wellington government finally succeeded in passing the Catholic Emancipation Act, despite defiant royal opposition.
Split into simpler sentences: Emancipation for Catholics was a core promise during the campaign for implementation of the Act of Union in 1801. Not until 1829 did the Wellington government finally succeeded in passing the Catholic Emancipation Act in the teeth of defiant royal opposition.