The system that evolved in Europe out of the collapse of the Roman Empire was

Gibbon is the correct answer as he is the author who first articulated the view that Christianity significantly contributed to the decline of the Roman Empire in his seminal work published in 1776. His thesis examines the interplay between the rise of Christianity and the weakening of Roman institutions and values.

Marie Jean Antoine Nicolas de Caritat, marquis de Condorcet, was a French philosopher and mathematician known for his work on social progress and democracy. He did not focus on the decline of the Roman Empire or attribute it to Christianity, making his contributions irrelevant to this specific historical analysis.

James Watt was a Scottish inventor and mechanical engineer known for his improvements to the steam engine. His work is unrelated to historical analyses of the Roman Empire or Christianity, placing him outside the context of this inquiry regarding the empire's decline.

James Boswell was a Scottish biographer and diarist best known for his biography of Samuel Johnson. His writings do not address the decline of the Roman Empire or the influence of Christianity, making him an incorrect option for this question.