"Do not think that he who loves his own country must hate and despise other nations, or wish for war, which is a remnant of barbarism. "- 
Patriotism is love of one’s country. Americans are usually patriotic. So are British people and people of other countries. Conservatives also like to imagine that liberals are not patriotic just because of negative opinions of war.
Patriotism is good
Most of the time patriotism is good because it encourages people to look after their countries rather than just being selfish. During World War II patriotic British people, patriotic American, patriotic Russians and others from the allied nations put their lives on the line to defend their nations against Hitler and Nazism. Liberals ought to be patriotic because it’s right to be unselfish, to look out for the best interests of one's neighbors and not just one's own.
When patriotism is bad
Patriotism can be the last refuge of a scoundrel. People pretend they’re patriotic when they just want to look after themselves and their own group. People pretend to be patriotic when they damage other countries. Really that’s unpatriotic because afterwards other countries don’t like your country and don’t mind damaging your country. A bad form of patriotism is thinking that your country is better and more important than the other countries. That is also known as extreme nationalism. There's less of this bad patriotism today than there was because we talk to people from other countries on the Internet. We see they're as good as we are, we see they matter as much as we do. The right wing of the American Republican Party is getting isolated as Mainstream Americans find on the Internet that people in other countries aren't like American right wingers.
Hitler and pretend patriotism
At first Hitler and the Nazis seemed to be patriotic, though they were fascist nationalists. They talked about making Germany great and defending Germany against imagined conspiracies. None of that worked out for Germany. The Nazis invaded other countries and hurt other people. The people the Nazis hurt fought back. Later in the Second World War it became obvious that Germany was losing. A real patriot would have tried to get out of the war with the best terms he could get. That wasn’t for Hitler. He was the Führer or leader and he was corrupted by power. Hitler was corrupt anyway. He didn’t mind destroying the whole German nation with millions of people but he couldn’t face defeat. Hitler forced the Germans to keep fighting a hopeless war with more and more people killed. Then he killed himself and didn’t have to face the consequences of his bad decisions.
Modern Conservatives claim to Patriotism
Since the neoliberal revolution in the United States, conservatives have made the claim that patriotism is solely the province of Conservatives. Neoliberals commonly claim that Patriotism isn't liberal and that Liberals are the opposite of Patriots.
There's certainly irony in the neoliberal claim to Patriotism, and it is entertaining to hear the claim made. Unfortunately neoliberals have discovered that large numbers of people are likely to believe any claim, made often enough with enough conviction. Too many people believe that the United States was originally conservative, or was founded to be a conservative Republic. Claims that the original American Patriots weren't Liberals, or that they or the enlightenment economic philosophers advocated unrestrained Capitalism or Laisez-Faire business practices of neoliberalism are the worst sort of revisionist Bullshit.
Original Patriots were mostly Liberals, and were fighting to continue the liberal progression from the Divine Right of Kings to the ideal of universal Human rights and self-government. Liberals, then, as now, disagreed on when and how to achieve progression to those ideals while maintaining the Liberal rights to life, liberty, and property. The original State Governments, and the United States government were a compromise between Liberals who desired immediate universal rights and democratic self-government and Liberals who desired representative self-government with universal rights and self government instituted as people became capable of fully participating in the government and economy.