My understanding: citizenship vs. ethnicity 我是俄罗斯人:I'm a citizen of the Russian Federation, but not necessary ethnically Russian.I could be a Tatar like Marat Safin or Ukrainian etc. 我是俄罗斯族:I'm ethnically Russian and might or might not be a Russian citizen. Russians are one of the 56 ethnic groups in China that has a popolution of around 15,000. Apart from ethnic groups, 族 could also mean a family or clan where most of the males share the same last name, or generally a class of things with common features or attributes(usually used as a scientific term e.g. 芳香族化合物 or a suffix of a buzzword e.g. 上班族

族,you can regard it as a nation.In China,there are 56 nations（民族). While,人，you can regard it "where are you from?",for example,you comes from Russia,so you are a 俄罗斯人。Can you understand?

族 это национальность, в основном для различения 56-ти китайских, но можно и для зарубежных... например 他_是_俄国人，但是_乌克兰_族。

族 = ethnic group 例: 中国著名歌唱家宋祖英是苗族人。

族 means there are lots of same things and they are stay together and become a kind of group. 族 = a kind of group. for example, 种族、家族 normally we say 俄罗斯人. 族 is not about country. for example, a chinese person, who has become an american citizen, cant be called 中国人 but we can call him 汉族人. there is no 美国族、英国人, but there are 美国人、英国人 a country name + 人 means the citizen of this country i dont know if 俄罗斯族 exists. if it exists, u can say 我是俄罗斯族。 if not, u can only say 我是俄罗斯人。