There are no end of stereotypes for and within every nationality, some more glaring than others, that surface often in fiction. An Irishman idly chewing on a raw potato, when there are other vittles to hand; an American Indian giving that celebrated war whoop; a meek, quiet Quaker. Now, there is no denying that the Irish ate potatoes, that some Indians had war cries, and that the Quakers, as a group, strove to be a mild people. But when these accepted facts begin to weigh down a book, it makes the subject matter grating.
In Martin Chuzzlewit, one of Dickens most celebrated novels, his characters Mark Tapley and Martin Chuzzlewit spend a great deal of time in America. They have come to seek their fortune in the relatively new nation of the United States, and they are hardly on shore before the stereotypes that made the book so controversial, begin. All but a handful of people wear straw hats, bear titles from the army (Colonel, Captain, Major, and so on), and, most glaring of all, talk a great deal about Liberty and Freedom and are absolute hypocrites. The irony comes in when these very same American characters stereotype the British people. Now, this portrayal of the United States is amusing for the first two or three pages, but stretched out over chapters upon chapters, it becomes galling.
The third book of Louisa May Alcott's series, Jo's Boys, provides some more such stereotypes. Emil is the sailor, and having fulfilled his dream of "sailing the ocean blue," he plays his role to the utmost. Everything is "jolly," everyone is a "land lubber," he walks with a swagger, he sings sailor songs, and uses terms like "weighing anchor" and "heave off." Alcott leaves out the harsher facts of navy life, like the floggings, the casualties, and the largely harsh and demanding captains. The result? Your stereotypical sailor.
Dan, the "firebrand" of Little Men, is a wanderer. On returning home from the West after nearly two years away, he is full of stories about Indians named Black Hawk and horses named Lightning and hunting buffalo; he brings back feathers and beads, tomahawks and moccasins and wampum (which were, incidentally, only used by the tribes of Eastern North America); and he teaches his companions to do the war whoop. For me, this went far to ruin Dan's character by giving him such time-worn stories to tell.
These sorts of stereotypes often slip into writing, and they may be large or they may be small. Some stereotypes are absolutely true and almost impossible to avoid - but I believe it weighs down the story when the author unconsciously makes major or minor characters "typical." Original characters are part of what gives spice to books, so it's good to think outside the box when developing them. If your story calls for a character who fits his nationality's stereotype, make sure you can pull it off without jarring the reader. Add a few interesting aspects to his or her background or personality. Ben-Hur's Messala, the Roman and the antagonist, is your typical Roman - proud, arrogant, and a Jew-hater. But not only is that acceptable because that character makes an excellent villain, but he has an original past: he grew up among the Jews. So add some spice to your characters and don't annoy your readers by feeding them stereotypes.