Cassandra row ordering best practice
I thought about another ColumnFamily "ArticlesByDateAndCountry" dynamic columns.


You're on the right track with this thought, but I'd stay away from dynamic columns.  Currently, there isn't a way to really manage column families with dynamic columns in CQL3.  So, the only real solution is to go the route of creating it in the cassandra-cli, which is being deprecated.  Sticking with CQL tables gives you a much easier path to data access, and that in itself (IMO) makes it worth it.  Besides, all the latest drivers work with CQL, so you're really backing yourself into a corner by choosing a path that can't be managed by it.

While it may not be readily apparent, there is a way to solve your current problem to adequately serve your queries.  I would build a (CQL) table, like this:

CREATE TABLE ArticlesByDateAndCountry (
 countrycode text,
 articledate timestamp,
 field1 text,
 field2 text,
 PRIMARY KEY ((countrycode),articledate))
WITH CLUSTERING ORDER BY (articledate DESC);


Note: I have created two sample payload fields, field1 and field2.  I'm sure your payload fields will vary.  Also, I have opted to use a timestamp instead of a timeuuid, as it makes the example easier. 

Essentially, this will group your data by countrycode.  And within each countrycode, your data will be sorted by articledate.

SELECT articledate, field1, field2
FROM ArticlesByDateAndCountry 
WHERE countrycode='US' 
AND articledate &gt;= '2015-01-23 00:00:00' AND articledate &lt; '2015-01-24 00:00:00';


You should read Patrick McFadin's article Getting started with Cassandra time series data modeling.  It has several examples that are quite similar to what you are doing here.  While I have demonstrated this with the timestamp type, you could very easily make this work with time UUIDs instead.  Here is a link to DataStax's documentation on Cassandra's timeuuid functions that I am sure you will find useful.