Complex sentence: In 1998, the United States intervened in the lawsuits on behalf of the plaintiffs in the claim in order for the claim to proceed against New York State in light of its assertion of its immunity from suit under the Eleventh Amendment to the United States Constitution.
Split into simpler sentences: In 1998, the United States intervened in the lawsuits on behalf of the plaintiffs in the claim so the claim could proceed against New York State. The state had asserted immunity from suit under the Eleventh Amendment to the United States Constitution.