I believe you mean the French involvement in the American Revolutionary War. The American Civil War was in the 1860s, while the American revolutionary war was in the 1770s-80s.

I think it would be best for everyone if you clarified the question. The American Civil War occurred from 1861 to 1865. The American Revolutionary War occurred from 1775 to 1783. To my knowledge France did not help during the American Civil War. Furthermore, the French Revolution occurred on again off again from 1792 to the early 1800s. Although it doesn't provide a direct answer to your question I hope it helps direct your research.

The massive debt that France got by providing support was a key reason there was unrest in France to begin with. This combined with food shortages led to the meeting of the estates general, which led to the revolution. That is the most direct influence that the Americans had on the French.

As far as the influence of American ideals on the French, there was some. Keep in mind that most of the French ideals at the time were driven by the enlightenment, just as the Americans were. The biggest thing to come out of the American Revolution was republicanism, a government with no king. This was a truly revolutionary concept, and some political groups in France liked it. The jacobins were the most famous, being on the far left, (literally the furthest on the left in the assembly, add well as being far left politically), and they were also led by the famous robespierre. They were the ones most adamant about killing the king. The girondist's were another republican group, but weren't as fervent about killing the king. A more direct connection to the American Revolution is seen here, as one of their allies was Thomas Paine, the pen of the American Revolution, author of common sense. He advocated for a government with no king, but didn't think the French should kill him. He was actually a member of the French government at the time, surprisingly enough. His other major work in France was the "Rights of man." Sound familiar? I know it was widely circulated, bit am unsure about its total impact on France. It was also rumored that he came up with the idea for his book after an evening with Jefferson and Lafayette.

Lafayette is another person looking into. He was a key figure in both revolutions, and was extremely close with Washington.