You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Napoleon

Context:
To expand his power, Napoleon used these assassination plots to justify the creation of an imperial system based on the Roman model. He believed that a Bourbon restoration would be more difficult if his family's succession was entrenched in the constitution. Launching yet another referendum, Napoleon was elected as Emperor of the French by a tally exceeding 99%. As with the Life Consulate two years earlier, this referendum produced heavy participation, bringing out almost 3.6 million voters to the polls.

Question:
What did Napoleon use to justify his creation of an imperial system?

assassination plots