Why 意大利 and not e.g., 意国 I always wondered why all main European countries are spelled in chinese with a Hanzi that identifies them or some about their origins more the 国 morpheme, 

Italy has a uncontested importance in European history, nevertheless its name has been just transliterated to 意大利, which IMHO reveals less participation in its codification.

Is it a matter of when the name was transposed to Chinese language? Maybe it's just the minor influence of the country in that period? I tried to search some information but I couldn't find anything (furthermore, my chinese level reading is extremely low).

UPDATE

The information and the page  suggested by @user2619 unfolded my research on the topic:

Seems like all the country names were just transliterated at first. The former name of the well know *什么*国 countries was, e.g.,:

美利坚 --&gt; 美国
法兰西 --&gt; 法国
日耳曼 --&gt; 德国
不列颠 --&gt; 英国
[...]


Later, above for all countries with more strict relations with China, these names were translated to a form more similar to 中国 possibly as a form of bigger respect.

I was teached at a chinese course that the particular 汉字 characherizing the country was somewhat chosen because of some historical reason. For example 法 for the country which invented the constitution. But chinese people I asked say this is not true and has to do with nothing but phonetic reasons. Then as seen in [1] in some case like 希腊， the sound is taken from the endonym rather than exonym.
It's just historical stuff. European countries that have commerce with China prior to the Ching dynasty and also modern countries after WWII, in general have fancier names.

希腊 for Greece
意大利 for Italy
瑞典 for Sweden
法国 for France
美国 for US
葡萄牙 for Portugal
马来西亚 for Malaysia
日本 for Japan


etc.

You just have to accept them as it is. It's hard to find a pattern why. 

Edit: http://www.nationsonline.org/oneworld/countrynames_chinese.htm

There's very few countries which have 国 in their names, it's more of a short form, like 英格兰 for 英国, 美利堅合眾國 for 美国. Others which have 共和国 in their names are People's Republic, like China, whose official name is People's Republic of China.