Yes, that's the rule regarding the deployment of AMISOM troops. That is why Ethiopia did not contribute troops. The troops can not be from a country that shares a border with the one they r to be stationed in. So the question is if Uganda and even Burundi sent troops to Somalia why did Tanzania not send troops too despite being impacted by al shabaab and the insecurity as much as Uganda and Burundi.
How much is the average Tanzanian Soldier paid?
What type of equipment does your army operate, do you have a navy? Do you have a true air force what type of planes do they have? Those are some of the questions any military asks itself before considering war. The finances to purchase the equipment and maintain a highly motivated and well paid force is of extreme importance.
In this case Tanzania is not is Somalia because with a $162 million budget for a > 30,000 strong military war is not a feasible option.
Regarding Japan in WWW II The only thing tiny about Japan was its size. Compared to the US it was a formidable force which had been in existence for thousands of years with a lot of money to spend and ability to produce planes, tanks, ships and bombs with ease. The only reason the US won was it was richer and bigger and therefore more modern.
In Chechnya, Russia has absolutely everything under control and to the contrary their brutal crackdown is what many complain about.
How many Somalis lost their lives vs the Americans in Somalia, how many American troops were there at that time and what was their mission and mandate????? The truth is evident one you see that.